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André Rosa Martins Int. Journal of Engineering Research and Applications www.ijera.com 
ISSN : 2248-9622, Vol. 4, Issue 11(Version - 5), November 2014, pp.101-112 
www.ijera.com 101 | P a g e 
Michaelis-Menten Kinetics in Transient State: Proposal for Reversible Inhibition Model and its Application on Enzymatic Hydrolysis of Disaccharides André Rosa Martins*, Lucas Oliveira** *(Campus Porto Alegre, Federal Institute of Rio Grande do Sul - IFRS, Porto Alegre, Brazil) 
**(Pure and Applied Mathematics Department, Federal University of Rio Grande do Sul - UFRGS, Porto Alegre, Brazil) 
ABSTRACT The enzymatic processes according Michaelis-Menten kinetics have been studied from various approaches to describe the inhibition state. Proposals for inhibition were compared from a generic process, where kinetic constants have received unitary values, and the numeric value of the concentration of substrate was ten (10) times higher than the numerical value of the concentration of enzyme. For each inhibition model proposed, numerical solutions were obtained from nonlinear system of ordinary differential equations, generating results presents by graphs showing the variation of the enzyme and enzyme complexes, also the variation of substrate and product of the reaction. Also, was designed a model with performance, indicating similar behavior to that seen in the Michaelis-Menten kinetics, where complex of reaction is rapidly formed and throughout the process, tends to decay to zero. Thus, in this new proposed model, the effect of inhibition starts at zero and, throughout the process, tends to the nominal value of the initial enzyme concentration. Such responses have proved to be valid for different values of enzyme concentration and process time, showing robustness. The proposed model was applied to the hydrolysis of disaccharides, providing a setting with conservation of mass of the model at the end of the process regarding the responses of the carbohydrate concentration. 
Keywords - enzymatic catalysis, kinetic model, Michaelis-Menten kinetics. 
I. INTRODUCTION 
More than 100 years after the publication of the emblematic work on enzyme kinetics of the inversion of sucrose disaccharide, by Leonor Michaelis and Muad Leonora Menten, the inhibition mechanism of the enzymatic catalysis processes on Michaelis-Menten kinetics is still not sufficiently clarified. In mathematical modeling for kinetics applied to most of enzymatic reactions, starts from Michaelis-Menten hypothesis, which describes the reaction rate in the condition where the substrate concentration is higher than the enzyme concentration and the sum of enzyme and enzyme complexes concentrations formed will remain constant throughout the processing time [1]. A major question regarding the process of enzyme-catalyzed reaction refers to the condition in which the inhibiting stage develops. The Michaelis- Menten kinetics does not contemplate the inhibition, even though the vast majority of enzymatic processes do not provide a 100% of substrate conversion, indicating that there is a point in which, for a given condition, the process is discontinued [2]. 
The literature on biochemistry shows four (4) possible mechanisms of reversible inhibition of enzymatic processes, known as: competitive; non- competitive; mixed and uncompetitive [3]. Also, solutions for general problem of steady- state enzyme kinetics have been limited in helping researchers, given that the generated models do not adequately fit the experimental observations. Inhibitors are traditionally characterized on assumption equilibrium in steady state, between the enzyme complex and the substrate reaction. According Fange et al. [4], this assumption would be valid only for very inefficient enzymes. Therefore, this study aims to assess the inhibition during the process, represented by Michaelis-Menten kinetics also it suggests new representations for catalysis in mathematical models on transient state representation. For that, it is applied a pictorial process for defining, where substrate concentration value is ten (10) times higher than the nominal value of enzyme concentration. The numerical solution of nonlinear systems of ordinary differential equations (ODE) was obtained by elaborating a routine in Matlab® with the method of Runge-Kutta 4th order. 
RESEARCH ARTICLE OPEN ACCESS
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ISSN : 2248-9622, Vol. 4, Issue 11(Version - 5), November 2014, pp.101-112 
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II. MICHAELIS-MENTEN KINETICS 
AND INHIBITTION MODELS 
For evaluating the different perspectives of 
inhibition, it is necessary, firstly, a careful approach 
of Michaelis-Menten kinetics applied to a generic 
process of catalysis, as described in Scheme 1. 
Scheme 1 - Michaelis-Menten kinetics 
E S ES E P 
k k 
k 
    
 
 
 
1 2 
1 
Where k1, k-1 and k2 are the kinetic constants of 
these reactions. The other components are: the 
concentration of enzyme (E), concentration of 
substrate (S), concentration of the enzyme-substrate 
complex (ES), and concentration of product (P). 
In mathematical modeling of preceding 
reactions, variations of substrate, enzyme, product 
and enzyme complex are obtained as follows: 
k ES k E S k ES 
dt 
dE 
1 1 2   (  )   
(1) 
k E S k ES k ES 
dt 
dES 
1 1 2  (  )    
(2) 
( ) 1 1 k ES k E S 
dt 
dS 
    
(3) 
k ES 
dt 
dP 
2  (4) 
For solution of the nonlinear system of 
ordinary differential equations described, the main 
requirement concerns the strict observance of the 
Law of Conservation of Mass for the enzyme and 
complex, by means the expression below: 
  E  ES  0 
dt 
d 
dt 
dES 
dt 
dE 
(5) 
In this model, the numerical solution is applied 
to the suggested pictorial process - shown in Figure 
1a - with carbohydrate concentration and enzyme 
hypothetical unit (X) representing a relation between 
mass and volume, also with process time on 
hypothetical unit (t). 
Figure 1a shows the variation of the enzyme 
and enzyme complex, and, on dotted line, the sum of 
contributions of these variables. Plus, Figure 1b 
shows the variation of substrate and product, and on 
dotted line, the sum of the contribution of these two 
components. 
It is noteworthy, that on dotted line in Figure 
1a the nominal value of the added enzyme remains, 
which is consistent with the Law of Conservation of 
Mass. And, on dotted line in Figure 1b it is possible 
to observe decay, in early stages, and eventually 
convergence to the nominal value of added substrate. 
Figure 1 - Response to the kinetic model of Scheme 1
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ISSN : 2248-9622, Vol. 4, Issue 11(Version - 5), November 2014, pp.101-112 
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This initial decay is linked to the relation 
between enzyme and substrate and it is equal to the 
ratio between these components. 
In the example shown, the fraction is equal to 
10/100, i.e., it represents an initial decay of 10% in 
the substrate and product sum, (compared with the 
process beginning), tending to the initial value of 
substrate concentration during the process. 
The complex reaction ES is formed immediately 
at the beginning of the reaction, and after that, 
decreases from an initial value, very close to the 
enzyme nominal value, to zero. During a significant 
part of the process, the variation of the complex 
concentration is small, what can indicate the 
possibility of considering this state as 'quasi-stationary', 
i.e.: 
 0 
dt 
dES 
(6) 
Furthermore, available current studies, usually, 
approaches the inhibition stage from this assumption: 
stationary or 'quasi-stationary' state, pointing an 
assumed balance between formation and dissociation 
of the enzyme substrate complex [5, 6, 7, 8]. 
A generic representation of the various 
possibilities to enzyme inhibition inversion is shown 
in Scheme 2, as proposed (modified) for Botts and 
Morales [9]. 
In this proposal two new enzymatic complexes 
are shown: EI representing inhibition complex and 
ESI representing the intermediate inhibition complex. 
Scheme 2 - Michaelis-Menten kinetics Mechanism of 
Inhibition 
Source: [10] 
In this general mechanism, it is also shown a 
substance I, which will be responsible for inhibition. 
In the Scheme 2, the coefficient  sets the ratio 
between the competitive and uncompetitive inhibition, 
and  is a multiplication factor of the kinetics' 
constant rate. 
The representation for ODEs system related to 
the general mechanism of Scheme 2 is shown below, 
and the Figure 2 shows a numerical solution of the 
system, from the pictorial model, and unit values for 
 and  . 
Figure 2 - Response to the generic mechanism of Scheme 2
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ISSN : 2248-9622, Vol. 4, Issue 11(Version - 5), November 2014, pp.101-112 
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k ES k (E S) k ES k EI S k (E S I ) 
dt 
dE 
S S p i i          (7) 
k (E S) k ES k ES k ESI k (ES I ) 
dt 
dES 
S S p i i        (8) 
k ES I k ESI k EI S k ESI k ESI 
dt 
dESI 
i i S S p  (  )   (  )   (9) 
k E S I k EI S k ESI k EI S k ESI 
dt 
dEI 
i i S S p  (   )     (  )   (10) 
k ES k (E S) k ESI k (EI S) 
dt 
dS 
S S S S       (11) 
k ES k ESI 
dt 
dP 
p p    (12) 
k EI S k (E S I ) k ESI k (ES I ) 
dt 
dI 
i i i i         (13) 
In this response, it is observed that the behavior 
of the enzyme and its complex is similar Michaelis- 
Menten kinetics without inhibition. 
In the Figure 2a the response indicates that ESI 
and EI complexes, remains equal to zero over the 
entire process time. Accordingly, in Figure 2b, the 
concentration of the inhibiting substance, also will 
remain equal to zero. 
Additionally, the observed response - in generic 
mechanism - will be repeated if, individually studied 
proposals for competitive, noncompetitive, mixed 
inhibition or uncompetitive. 
Furthermore, another way to represent the 
process of inhibition is considering the inhibitor as a 
product of the reaction, as shown in Scheme 3. Figure 
3 shows results for process with product inhibition, 
where: k1 = k2 = 3, and the other constant unitary. 
Scheme 3 - Michaelis-Menten kinetics with product 
inhibition 
E S ES E P EP 
k 
k 
k k 
k 
 
 
 
 
 
 
     
3 
3 
1 2 
1 
Source: [11] 
Figure 3 Response kinetic model of Scheme 3
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( ) ( ) 1 1 2 3 3 k ES k E S k ES k EP k E P 
dt 
dE 
         
(14) 
k E S k ES k ES 
dt 
dES 
1 1 2  (  )    
(15) 
k E P k EP 
dt 
dEP 
3 3 ( )     (16) 
( ) 1 1 k ES k E S 
dt 
dS 
    
(17) 
( ) 2 3 3 k ES k EP k E P 
dt 
dP 
     
(18) 
The result shown in Figure 3b may be observed 
that there is no convergence of the product to the 
initial value of the substrate at the end of the process, 
as observed in Michaelis-Menten kinetics with 
inhibition - Scheme 2. 
In the model with product inhibition, proposed 
in Scheme 3, a percentage error, at the end of the 
process occurs (Ef (%)) and it is equivalent to 
enzyme-substrate ratio (ESR), i.e.: 
S 
E 
ESR  → E (%)  ESR 100 f (19) 
In the Figure 3a, it is observed that ES is 
instantly formed, and during the process, it decays, 
tending to zero. The complex EP, on the other hand, 
increases from zero and tends to the initial value of 
enzyme. 
The free enzyme (E) instantly decays to zero and 
remains near that value throughout the process, 
resulting in: 
dt 
dES 
dt 
dEP 
  (20) 
Specifically, for the hydrolysis of sucrose by the 
enzyme invertase - firstly studied and published in 
1913 by Michaelis and Menten - recently, Johnson and 
Goody [1] - have proposed a framework for the 
product inhibition hypothesis, where S is sucrose, G is 
glucose, F is fructose, EG is the glucose-enzyme 
complex and EF represents the fructose-enzyme 
complex. 
Representation for such process is shown by 
Johnson [12], according Scheme 4. 
Scheme 4 - Model of sucrose inversion with inhibition 
by products 
Source: [12] 
Figure 4 shows the result of the pictorial process 
according Johnson [12] model in the same conditions, 
for the system of ordinary differential equations - on 
model of Scheme 4, as shown below: 
( ) ( ) ( ) ( ) ( ) 1 1 5 5 6 6 k ES k E S k EF G k E F G k EG F k E F G 
dt 
dE 
                
(21) 
( ) ( ) ( ) 4 4 6 6 k EFG k EG F k E F G k EG F 
dt 
dEG 
          
(22) 
( ) ( ) ( ) 3 3 5 5 k EFG k EF G k E F G k EF G 
dt 
dEF 
          
(23) 
k E S k ES k EFG k ES 
dt 
dES 
1 1 2 2  (  )      
(24) 
k ES k EFG k EF G k EFG k EG F k EFG 
dt 
dEFG 
2 2 3 3 4 4    (  )   (  )     
(25) 
( ) 1 1 k ES k E S 
dt 
dS 
    
(26) 
( ) 0,5( )( ) 0,5 ( ) 0,5 ( ) 4 4 6 5 5 6 k EFG k EG F k k E F G k EF G k EG F 
dt 
dF 
              
(27) 
( ) 0,5( )( ) 0,5 ( ) 0,5 ( ) 3 3 5 6 6 5 k EFG k EF G k k E F G k EG F k EF G 
dt 
dG 
              
(28)
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Figure 4 - Response of kinetic model on Scheme 4 
It is possible to note in Figure 4b the response in which the range of the product indicates the tendency for obtaining the same numerical values for concentrations of glucose and fructose. In Figure 4a, it is shown the complex reaction (ES) slowly tending to zero, while complex of inhibition (EI) tends even slower to the numerical value of the initial substrate concentration. The response of Johnson [12] model, however, keeps the behavior observed in the van Boekel [11] model, which refers to the error associated with the numerical value of the ratio percentage of the enzyme substrate. 
III. PROPOSAL FOR A NEW MODEL 
In order to design a model aiming to represent the effect of inhibition on Michaelis-Menten kinetics it is necessary, firstly, to establish some assumptions: 
a. Continuously, and throughout the process time, the model should strictly follow the Law of Conservation of Mass, regarding to the variation of enzyme and its complexes sum; 
b. The model should converge the substrate and product sum to the nominal value of the added substrate, in a high enough time and with the lowest error (as possible) to ensure stability to the process; 
c. To ensure the process stability, the model must be sufficiently robust, so, allowing variation on the ratio enzyme - substrate, in the longest possible time; 
d. The model should facilitate a performance of reaction complex (enzyme substrate complex) with a high rate at the beginning of reaction, and decreasing overtime, tending to zero at the end of the process; 
e. The model should represent the effect of inhibition from a enzyme complex which can act on the complex reaction, thus indicating its relation with other components of the enzymatic catalysis; 
f. In case of more than one enzymatic complex and more than one product of reaction, its contributes should be considered for the purpose of inhibition; 
g. The model should provide an initial formation of the inhibition complex equal to zero, increasing overtime and tending to the initial value of the enzyme at the end of the process. 
As follow, it is applied the aforementioned premises to a process of enzymatic reaction, in which a generic substrate, S is converted to two (2) products with equal molecular weight, PI and PII typical representation of hydrolysis of disaccharides. Scheme 5 presents the proposal such model.
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In this proposal, it is both formed a reaction 
complex with the substrate (ES) as a complex with 
one of the products (EPI) also, the representation of 
inhibition complex (EI). 
Scheme 5 - Proposed model for the inhibition of 
enzymatic hydrolysis of disaccharides 
I II 
k k 
k 
E  SES EP  P 
 
 
 
1 2 
1 
(A) 
I 
k 
k 
I EP E  P 
 
 
 
3 
3 
(B) 
I II 
k 
k 
k 
k 
I II EP P EI E P P 
ii 
ii 
i 
i 
     
 
 
 
 
 
 
(C) 
In the Scheme 5 the stage (A) is the initial 
reaction, according to Michaelis-Menten kinetic. 
The stage (B) represented the hydrolysis process 
and the stage (C) represented the inhibition process. 
The proposed model assumes the mechanism of 
inhibition by the product to express the catalysis 
stage, asserting that inhibition effect occurs on the 
reaction complex (ES) forming a complex of 
inhibition (EI). 
The complex of inhibition is related to the free 
enzyme (E), with enzyme-product complex (EPI) and 
with the hydrolysis products (PI and PII), respecting 
the stoichiometry of the reaction. 
This is a competitive type of inhibition, by both 
reaction products and uncompetitive inhibition by 
reaction product that has no affinity to form a 
complex with the enzyme (in this case PII). 
Thus, the model designs a nonlinear system with 
seven (7) ordinary differential equations and nine (9) 
kinetic constants. Figure 5 shows the numerical 
results for the generic process. 
Figure 5 Response of the generic process for the enzymatic hydrolysis of disaccharides 
  I I ii ii I II k ES k E S k EP k E P k EI k E P P 
dt 
dE 
             ( ) ( ) 1 1 3 3 
(29) 
( ) ( ) 2 3 I 3 I i i I II 
I k ES k E P k EP k EI k EP P 
dt 
dEP 
         
(30)
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k E S k ES k ES 
dt 
dES 
1 1 2  (  )    
(31) 
k E P P k EI k EP P k EI 
dt 
dEI 
ii I II ii i I II i         ( ) ( ) (32) 
( ) 1 1 k ES k E S 
dt 
dS 
    
(33) 
( ) 0,5 0,5 ( ) 3 I 3 I ii ii I II 
I k EP k E P k EI k E P P 
dt 
dP 
           
(34) 
0,5 0,5 ( ) ( ) 2 ii ii I II i i I II 
II k ES k EI k E P P k EI k EP P 
dt 
dP 
            
(35) 
The Figure 5b presents the expected behavior for 
a reaction process in which a substrate is divided into 
two products of equal molecular mass. 
At the beginning of the reaction there is a 
fluctuation, showing a concentration of PII slightly 
higher than the PI but throughout the process was 
observed a tendency of obtaining approximate 
concentrations of both products. 
Figure 5a shows the trend of increasing complex 
of inhibition and the consequent reduction of the 
reaction complex, with an initial fluctuation of the 
enzyme-product complex. 
This fluctuation on enzyme-product complex 
variation is associated, apparently, to the difference in 
the initial fluctuation of products concentration in the 
graph (Figure 5b). 
IV. RESULTS AND DISCUSSION 
The conservation of mass of the model (CMM) - 
throughout the process - was calculated according the 
following expression, where yi is the value of each 
carbohydrate concentration overtime and V is the 
different carbohydrate in the system. 
The value of the error - at the end of the process 
(Ef) - for not being linked to the enzyme substrate 
ratio (ESR) was calculated by comparing the 
numerical value of the initial substrate (S0) with the 
conservation of mass at the endpoint of the process. 
( ) 
1  
 
V 
i 
i CMM y ; ( ( 1)) 
1 
0     
V 
i 
f i E S y n (36) 
Figure 6 shows the result for the model proposal 
in this work only to substrate and products variation. 
Figure 6 - Response for variation of substrate and products
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Figure 7 - Response of hydrolysis of disaccharides with increment in time 
Figure 7 shows the result, for the model 
designed in this work, when the numerical value of 
the process time is increased ten times, maintaining 
other parameters equal to those in Figure 6. 
Additionally, it is observed that the sum of 
carbohydrate, at the end of the process in Figure 7, 
have a significantly lower error compared to the 
results obtained in the error of Figure 6. 
In order to check the error associated with the 
proposed model, and view the initial fluctuation in 
concentration of product, Figure 6 and Figure 7 shows 
the result only by changing the carbohydrate along the 
generic process, keeping the enzyme substrate ratio 
(ESR) equal to 0.1 (S = 100 and E = 10). 
Thus, it is possible to observe that the error, 
calculated at the end of the process, was 2.6122 and 
0.3963, respectively to Figure 6 and Figure 7, and 
therefore, not related to the percentage ratio of 
enzyme-substrate, such as the inhibition presented by 
Johnson [12]. 
In the graph of Figure 7, it is seen a trend for 
error decay overtime, which allows us to infer the 
existence of a set of numerical values for the kinetic 
constants, which provide an error close to zero in a 
given process time. 
Thus, the situation indicates that the model, 
despite a proposal of product inhibition, differs from 
the behavior observed in Johnson [12], which was 
designed to represent the process of hydrolysis of 
sucrose disaccharides. 
Figure 8 shows the numerical results for the 
generic process S = 100, E = 10 and t = 20, foreseeing 
the conservation of mass of carbohydrates at the end 
of process. 
This response is shown the result with complete 
substrate conversion, keeping the same process time 
conditions and concentrations of substrate and 
enzyme shown in Figure 6. The numerical values of 
the kinetic constants, in Figure 8, were k1 = 165, k2 = 
k-1 = 70, other constants with numerical values equal 
to ten (10). 
The response, in Figure 8, shows - for the 
reaction products, the theoretical behavior expected 
for such enzymatic processes, with first order 
catalysis - kinetics in the beginning of the process, 
and at the end of the process, zero-order, i.e., it can be 
described (the reaction velocity) (v) as: 
dt 
dP 
dt 
dS 
v    → 
dt 
dP 
dt 
dP 
dt 
dS 
v I II     (37) 
Thus, it can be described as follow: 
 ( ) ( ) ( ) ( ) 1 1 3 I 3 I 2 ii ii I II i i I II  k ES  k E  S  k EP  k E  P  k ES  k EI  k E  P  P  k EI  k EP  P     
k E S k E P k EP k EP P k E P P k k EI  
k k 
ES I I i I II ii I II i ii ( ) ( ) ( ) ( ) ( ) 
1 
1 3 3 
1 2 
   
 
           
 
 (38)
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The Michaelis-Menten constant ( M k ), widely known, was applied to the equation ES: 
1 
1 2 
k 
k k 
kM 
 
  (39) 
k E P k EP k EP P k E P P k k EI  
k k k 
E S 
ES I I i I II ii I II i ii 
M 
( ) ( ) ( ) ( ) 
( ) 1 
3 3 
1 2 
   
 
         
 
 
 
 (40) 
Hereafter, is postulated the existence of one kinetic constant for hydrolysis (kH) in step, assuming equal 
numerical values for the rate of this process stage, and also a single constant in the inhibition stage (kI) assuming 
equal constant numerical values for the effect of inhibition as follows: 
h k  k  k 3 3 → 
h 
H k 
k k 
k 1 2  
  (41) 
i i ii ii in k  k  k  k  k   → 
in 
I k 
k k 
k 1 2  
  (42) 
By applying the expressions of the hydrolysis and inhibition constant, in the equation representing ES, we 
have: 
    
I 
I II I II 
H 
I I 
M k 
EP P E P P EI 
k 
E P EP 
k 
E S 
ES 
( ) ( ) (  )  (   )  2 
 
  
 
 
 (43) 
Figure 8 - Response for hydrolysis of disaccharides with full conversion 
Finally, it was assessed if the model is 
sufficiently robust to the situation in which both 
enzyme substrate ratio (ESR) and process time are 
modified. 
Thus, the example of enzymatic hydrolysis of 
sucrose by invertase, originally studied by Michaelis 
and Menten is considered. Scheme 6 shows the model 
for the reaction shown in Figure 9, assuming that there 
is affinity of the enzyme to form a complex with 
glucose exclusively. 
Figure 9 shows the response to the process 
condition in which the numerical value of the 
substrate concentration was equal to 50 and the 
numerical value of the concentration of the enzyme 
was equal to 0.42. The numerical value of the process 
time was equal to 330.
André Rosa Martins Int. Journal of Engineering Research and Applications www.ijera.com 
ISSN : 2248-9622, Vol. 4, Issue 11(Version - 5), November 2014, pp.101-112 
www.ijera.com 111 | P a g e 
Scheme 6 - Proposed model for the inhibition of enzymatic hydrolysis of sucrose 
E S ES EG F 
k k 
k 
    
 
 
 
1 2 
1 
(Initial stage of reaction) 
EG E G 
k 
k 
  
 
 
 
3 
3 
(Hydrolysis stage) 
EG F EI E G F 
ii 
ii 
i 
i 
k 
k 
k 
k 
     
 
 
 
 
 
 
(Inhibition stage) 
Figure 9 - Response of enzymatic hydrolysis of sucrose 
Figure 9 shows the response to the process 
condition in which the numerical value of the 
substrate concentration was equal to 50 and the 
numerical value of the concentration of the enzyme 
was equal to 0.42. 
The numerical value of the process time was 
equal to 330. In this model, the inhibition effect 
occurs from the increased concentrations of the 
products, competitive inhibition for glucose and 
fructose and uncompetitive inhibition for fructose. 
The enzyme substrate ratio (ESR) was equal to 
0.0084, considering that, in previous ratios, was 0.1. 
Numerical values of the kinetic constants, for the 
adjustment shown in Figure 9 are: k1 = 5.50; k-1 = 
5.32; k2 = 3.87; k3 = k-3 = 1.06; and ki = k-i = kii = k-ii = 
50. 
The response on Figure 9 shows that reducing 
the amount of enzyme-substrate ratio (ESR) it tends to 
minimize fluctuations previously observed at the 
initial stage of products reaction, as regards the 
behavior of the model in this model. 
For Scheme 6, the equation representing 
variation of the complex reaction is shown as: 
    
M H I k 
EG F E G F EI 
k 
E G EG 
k 
E S 
ES 
( ) ( ) (  )  (   )  2 
 
  
 
 
 (44)
André Rosa Martins Int. Journal of Engineering Research and Applications www.ijera.com 
ISSN : 2248-9622, Vol. 4, Issue 11(Version - 5), November 2014, pp.101-112 
www.ijera.com 112 | P a g e 
Also, numerical values for the adjustment shown in Figure 9, in relation to the kinetic constants of hydrolysis of inhibition by Michaelis-Menten were: kM = 1.67; kH = 8.67 and kI = 0.18. 
V. CONCLUSION 
In this work, the inhibition stage of enzymatic reaction, represented by Michaelis-Menten kinetics, had its behavior described, by applying the proposed inhibition - increasing the concentration of the product in numerical solution of a generic process. The new model was applied on the enzymatic process that generated two (2) reaction products, both with equal molecular mass - in the case of hydrolysis of disaccharides. 
Unlike the current models which present inhibition by product, and provide an error linked to the percentage of the enzyme-substrate fraction; the aim of this work, combining competitive and uncompetitive inhibition, was allow to reach a result that minimizes the percentage error, and could provide conservation of mass to the sum of the substrate and products - after proper adjustment of the numerical values of the kinetic constants. Moreover, the model was robust concerning the variation ratio of the enzyme-substrate, also during the time process variation. Concluding, application of this approach - inhibition effect in the construction of new models - should be differentiated and applied to each specific situation, especially in cases of enzymatic catalysis that generate different reaction products. 
REFERENCES 
[1] K.A. Johnson; R.S. Goody, The original Michaelis constant: translation of the 1913 Michaelis-Menten paper. Biochemistry, v. 50, 2011, p. 8264-8269. 
[2] S. Chaudhury; O.A. Igoshin, Dynamic disorder in quasi-equilibrium enzymatic systems. PLoS ONE, v. 8, 2010, e12364. 
[3] IUB - International Union of Biochemistry. Symbolism and terminology in enzyme kinetics. Recommendations 1981. European Journal of Biochemistry, v. 128, 1982, p. 281-291. 
[4] D. Fange; M. Lovmar; M.Y. Pavlov; M. Ehrenberg, Identification of enzyme inhibitory mechanisms from steady-state kinetics. Biochimie, v. 93, 2011, p. 1623- 1629. 
[5] A.R. Tzafriri; E.R. Edelman, Quasi-steady state kinetics at enzyme and substrate concentrations in excess of the Michaelis- Menten constant. Journal of Theoretical Biology, v. 245, 2007, p. 737-748. 
[6] I. Stoleriu; F.A. Davidson; J.L. Liu, Quasi- steady state assumptions for non-isolated enzyme-catalysed reactions. Journal of Mathematics Biology, v. 48, 2004, p. 82-104. 
[7] M.I. Recht; F.E. Torres; D.D. Bruyker; A.G. Bell; M. Klumpp; R.H. Bruce, Measurement of enzyme kinetics and inhibitor constants using enthalpy arrays. Analytical Biochemistry, v. 388, 2009, p. 204-212. 
[8] E. Bakalis; M. Kosmas; E.M Papamichael, Perturbation theory in the catalytic rate constant of the Henry-Michaelis-Menten enzymatic reaction. Bulletin of Mathematical Biology, v. 74, 2012, p. 2535-2546. 
[9] J. Botts; M. Morales, Analytical description of the effects of modifiers and of enzyme multivalency upon the steady state catalyzed reaction rate. Transactions of the Faraday Society, v. 49, 1953, p. 696-707. 
[10] P. Schenker; A. Baici, Simultaneous interaction of enzymes with two modifiers: reappraisal of kinetic models and new paradigms. Journal of Theoretical Biology, v. 261, 2009, p. 318-329. 
[11] M.A.J.S. van Boekel, Kinetic modeling of reaction in foods. New York (USA): CRC Press, 2009. 788p. 
[12] K.A. Johnson, Review: A century of enzyme kinetic analysis, 1913 to 2013. FEBS Letters, v. 587, 2013, p. 2753-2766.

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Michaelis-Menten Kinetics in Transient State: Proposal for Reversible Inhibition Model and its Application on Enzymatic Hydrolysis of Disaccharides

  • 1. André Rosa Martins Int. Journal of Engineering Research and Applications www.ijera.com ISSN : 2248-9622, Vol. 4, Issue 11(Version - 5), November 2014, pp.101-112 www.ijera.com 101 | P a g e Michaelis-Menten Kinetics in Transient State: Proposal for Reversible Inhibition Model and its Application on Enzymatic Hydrolysis of Disaccharides André Rosa Martins*, Lucas Oliveira** *(Campus Porto Alegre, Federal Institute of Rio Grande do Sul - IFRS, Porto Alegre, Brazil) **(Pure and Applied Mathematics Department, Federal University of Rio Grande do Sul - UFRGS, Porto Alegre, Brazil) ABSTRACT The enzymatic processes according Michaelis-Menten kinetics have been studied from various approaches to describe the inhibition state. Proposals for inhibition were compared from a generic process, where kinetic constants have received unitary values, and the numeric value of the concentration of substrate was ten (10) times higher than the numerical value of the concentration of enzyme. For each inhibition model proposed, numerical solutions were obtained from nonlinear system of ordinary differential equations, generating results presents by graphs showing the variation of the enzyme and enzyme complexes, also the variation of substrate and product of the reaction. Also, was designed a model with performance, indicating similar behavior to that seen in the Michaelis-Menten kinetics, where complex of reaction is rapidly formed and throughout the process, tends to decay to zero. Thus, in this new proposed model, the effect of inhibition starts at zero and, throughout the process, tends to the nominal value of the initial enzyme concentration. Such responses have proved to be valid for different values of enzyme concentration and process time, showing robustness. The proposed model was applied to the hydrolysis of disaccharides, providing a setting with conservation of mass of the model at the end of the process regarding the responses of the carbohydrate concentration. Keywords - enzymatic catalysis, kinetic model, Michaelis-Menten kinetics. I. INTRODUCTION More than 100 years after the publication of the emblematic work on enzyme kinetics of the inversion of sucrose disaccharide, by Leonor Michaelis and Muad Leonora Menten, the inhibition mechanism of the enzymatic catalysis processes on Michaelis-Menten kinetics is still not sufficiently clarified. In mathematical modeling for kinetics applied to most of enzymatic reactions, starts from Michaelis-Menten hypothesis, which describes the reaction rate in the condition where the substrate concentration is higher than the enzyme concentration and the sum of enzyme and enzyme complexes concentrations formed will remain constant throughout the processing time [1]. A major question regarding the process of enzyme-catalyzed reaction refers to the condition in which the inhibiting stage develops. The Michaelis- Menten kinetics does not contemplate the inhibition, even though the vast majority of enzymatic processes do not provide a 100% of substrate conversion, indicating that there is a point in which, for a given condition, the process is discontinued [2]. The literature on biochemistry shows four (4) possible mechanisms of reversible inhibition of enzymatic processes, known as: competitive; non- competitive; mixed and uncompetitive [3]. Also, solutions for general problem of steady- state enzyme kinetics have been limited in helping researchers, given that the generated models do not adequately fit the experimental observations. Inhibitors are traditionally characterized on assumption equilibrium in steady state, between the enzyme complex and the substrate reaction. According Fange et al. [4], this assumption would be valid only for very inefficient enzymes. Therefore, this study aims to assess the inhibition during the process, represented by Michaelis-Menten kinetics also it suggests new representations for catalysis in mathematical models on transient state representation. For that, it is applied a pictorial process for defining, where substrate concentration value is ten (10) times higher than the nominal value of enzyme concentration. The numerical solution of nonlinear systems of ordinary differential equations (ODE) was obtained by elaborating a routine in Matlab® with the method of Runge-Kutta 4th order. RESEARCH ARTICLE OPEN ACCESS
  • 2. André Rosa Martins Int. Journal of Engineering Research and Applications www.ijera.com ISSN : 2248-9622, Vol. 4, Issue 11(Version - 5), November 2014, pp.101-112 www.ijera.com 102 | P a g e II. MICHAELIS-MENTEN KINETICS AND INHIBITTION MODELS For evaluating the different perspectives of inhibition, it is necessary, firstly, a careful approach of Michaelis-Menten kinetics applied to a generic process of catalysis, as described in Scheme 1. Scheme 1 - Michaelis-Menten kinetics E S ES E P k k k        1 2 1 Where k1, k-1 and k2 are the kinetic constants of these reactions. The other components are: the concentration of enzyme (E), concentration of substrate (S), concentration of the enzyme-substrate complex (ES), and concentration of product (P). In mathematical modeling of preceding reactions, variations of substrate, enzyme, product and enzyme complex are obtained as follows: k ES k E S k ES dt dE 1 1 2   (  )   (1) k E S k ES k ES dt dES 1 1 2  (  )    (2) ( ) 1 1 k ES k E S dt dS     (3) k ES dt dP 2  (4) For solution of the nonlinear system of ordinary differential equations described, the main requirement concerns the strict observance of the Law of Conservation of Mass for the enzyme and complex, by means the expression below:   E  ES  0 dt d dt dES dt dE (5) In this model, the numerical solution is applied to the suggested pictorial process - shown in Figure 1a - with carbohydrate concentration and enzyme hypothetical unit (X) representing a relation between mass and volume, also with process time on hypothetical unit (t). Figure 1a shows the variation of the enzyme and enzyme complex, and, on dotted line, the sum of contributions of these variables. Plus, Figure 1b shows the variation of substrate and product, and on dotted line, the sum of the contribution of these two components. It is noteworthy, that on dotted line in Figure 1a the nominal value of the added enzyme remains, which is consistent with the Law of Conservation of Mass. And, on dotted line in Figure 1b it is possible to observe decay, in early stages, and eventually convergence to the nominal value of added substrate. Figure 1 - Response to the kinetic model of Scheme 1
  • 3. André Rosa Martins Int. Journal of Engineering Research and Applications www.ijera.com ISSN : 2248-9622, Vol. 4, Issue 11(Version - 5), November 2014, pp.101-112 www.ijera.com 103 | P a g e This initial decay is linked to the relation between enzyme and substrate and it is equal to the ratio between these components. In the example shown, the fraction is equal to 10/100, i.e., it represents an initial decay of 10% in the substrate and product sum, (compared with the process beginning), tending to the initial value of substrate concentration during the process. The complex reaction ES is formed immediately at the beginning of the reaction, and after that, decreases from an initial value, very close to the enzyme nominal value, to zero. During a significant part of the process, the variation of the complex concentration is small, what can indicate the possibility of considering this state as 'quasi-stationary', i.e.:  0 dt dES (6) Furthermore, available current studies, usually, approaches the inhibition stage from this assumption: stationary or 'quasi-stationary' state, pointing an assumed balance between formation and dissociation of the enzyme substrate complex [5, 6, 7, 8]. A generic representation of the various possibilities to enzyme inhibition inversion is shown in Scheme 2, as proposed (modified) for Botts and Morales [9]. In this proposal two new enzymatic complexes are shown: EI representing inhibition complex and ESI representing the intermediate inhibition complex. Scheme 2 - Michaelis-Menten kinetics Mechanism of Inhibition Source: [10] In this general mechanism, it is also shown a substance I, which will be responsible for inhibition. In the Scheme 2, the coefficient  sets the ratio between the competitive and uncompetitive inhibition, and  is a multiplication factor of the kinetics' constant rate. The representation for ODEs system related to the general mechanism of Scheme 2 is shown below, and the Figure 2 shows a numerical solution of the system, from the pictorial model, and unit values for  and  . Figure 2 - Response to the generic mechanism of Scheme 2
  • 4. André Rosa Martins Int. Journal of Engineering Research and Applications www.ijera.com ISSN : 2248-9622, Vol. 4, Issue 11(Version - 5), November 2014, pp.101-112 www.ijera.com 104 | P a g e k ES k (E S) k ES k EI S k (E S I ) dt dE S S p i i          (7) k (E S) k ES k ES k ESI k (ES I ) dt dES S S p i i        (8) k ES I k ESI k EI S k ESI k ESI dt dESI i i S S p  (  )   (  )   (9) k E S I k EI S k ESI k EI S k ESI dt dEI i i S S p  (   )     (  )   (10) k ES k (E S) k ESI k (EI S) dt dS S S S S       (11) k ES k ESI dt dP p p    (12) k EI S k (E S I ) k ESI k (ES I ) dt dI i i i i         (13) In this response, it is observed that the behavior of the enzyme and its complex is similar Michaelis- Menten kinetics without inhibition. In the Figure 2a the response indicates that ESI and EI complexes, remains equal to zero over the entire process time. Accordingly, in Figure 2b, the concentration of the inhibiting substance, also will remain equal to zero. Additionally, the observed response - in generic mechanism - will be repeated if, individually studied proposals for competitive, noncompetitive, mixed inhibition or uncompetitive. Furthermore, another way to represent the process of inhibition is considering the inhibitor as a product of the reaction, as shown in Scheme 3. Figure 3 shows results for process with product inhibition, where: k1 = k2 = 3, and the other constant unitary. Scheme 3 - Michaelis-Menten kinetics with product inhibition E S ES E P EP k k k k k            3 3 1 2 1 Source: [11] Figure 3 Response kinetic model of Scheme 3
  • 5. André Rosa Martins Int. Journal of Engineering Research and Applications www.ijera.com ISSN : 2248-9622, Vol. 4, Issue 11(Version - 5), November 2014, pp.101-112 www.ijera.com 105 | P a g e ( ) ( ) 1 1 2 3 3 k ES k E S k ES k EP k E P dt dE          (14) k E S k ES k ES dt dES 1 1 2  (  )    (15) k E P k EP dt dEP 3 3 ( )     (16) ( ) 1 1 k ES k E S dt dS     (17) ( ) 2 3 3 k ES k EP k E P dt dP      (18) The result shown in Figure 3b may be observed that there is no convergence of the product to the initial value of the substrate at the end of the process, as observed in Michaelis-Menten kinetics with inhibition - Scheme 2. In the model with product inhibition, proposed in Scheme 3, a percentage error, at the end of the process occurs (Ef (%)) and it is equivalent to enzyme-substrate ratio (ESR), i.e.: S E ESR  → E (%)  ESR 100 f (19) In the Figure 3a, it is observed that ES is instantly formed, and during the process, it decays, tending to zero. The complex EP, on the other hand, increases from zero and tends to the initial value of enzyme. The free enzyme (E) instantly decays to zero and remains near that value throughout the process, resulting in: dt dES dt dEP   (20) Specifically, for the hydrolysis of sucrose by the enzyme invertase - firstly studied and published in 1913 by Michaelis and Menten - recently, Johnson and Goody [1] - have proposed a framework for the product inhibition hypothesis, where S is sucrose, G is glucose, F is fructose, EG is the glucose-enzyme complex and EF represents the fructose-enzyme complex. Representation for such process is shown by Johnson [12], according Scheme 4. Scheme 4 - Model of sucrose inversion with inhibition by products Source: [12] Figure 4 shows the result of the pictorial process according Johnson [12] model in the same conditions, for the system of ordinary differential equations - on model of Scheme 4, as shown below: ( ) ( ) ( ) ( ) ( ) 1 1 5 5 6 6 k ES k E S k EF G k E F G k EG F k E F G dt dE                 (21) ( ) ( ) ( ) 4 4 6 6 k EFG k EG F k E F G k EG F dt dEG           (22) ( ) ( ) ( ) 3 3 5 5 k EFG k EF G k E F G k EF G dt dEF           (23) k E S k ES k EFG k ES dt dES 1 1 2 2  (  )      (24) k ES k EFG k EF G k EFG k EG F k EFG dt dEFG 2 2 3 3 4 4    (  )   (  )     (25) ( ) 1 1 k ES k E S dt dS     (26) ( ) 0,5( )( ) 0,5 ( ) 0,5 ( ) 4 4 6 5 5 6 k EFG k EG F k k E F G k EF G k EG F dt dF               (27) ( ) 0,5( )( ) 0,5 ( ) 0,5 ( ) 3 3 5 6 6 5 k EFG k EF G k k E F G k EG F k EF G dt dG               (28)
  • 6. André Rosa Martins Int. Journal of Engineering Research and Applications www.ijera.com ISSN : 2248-9622, Vol. 4, Issue 11(Version - 5), November 2014, pp.101-112 www.ijera.com 106 | P a g e Figure 4 - Response of kinetic model on Scheme 4 It is possible to note in Figure 4b the response in which the range of the product indicates the tendency for obtaining the same numerical values for concentrations of glucose and fructose. In Figure 4a, it is shown the complex reaction (ES) slowly tending to zero, while complex of inhibition (EI) tends even slower to the numerical value of the initial substrate concentration. The response of Johnson [12] model, however, keeps the behavior observed in the van Boekel [11] model, which refers to the error associated with the numerical value of the ratio percentage of the enzyme substrate. III. PROPOSAL FOR A NEW MODEL In order to design a model aiming to represent the effect of inhibition on Michaelis-Menten kinetics it is necessary, firstly, to establish some assumptions: a. Continuously, and throughout the process time, the model should strictly follow the Law of Conservation of Mass, regarding to the variation of enzyme and its complexes sum; b. The model should converge the substrate and product sum to the nominal value of the added substrate, in a high enough time and with the lowest error (as possible) to ensure stability to the process; c. To ensure the process stability, the model must be sufficiently robust, so, allowing variation on the ratio enzyme - substrate, in the longest possible time; d. The model should facilitate a performance of reaction complex (enzyme substrate complex) with a high rate at the beginning of reaction, and decreasing overtime, tending to zero at the end of the process; e. The model should represent the effect of inhibition from a enzyme complex which can act on the complex reaction, thus indicating its relation with other components of the enzymatic catalysis; f. In case of more than one enzymatic complex and more than one product of reaction, its contributes should be considered for the purpose of inhibition; g. The model should provide an initial formation of the inhibition complex equal to zero, increasing overtime and tending to the initial value of the enzyme at the end of the process. As follow, it is applied the aforementioned premises to a process of enzymatic reaction, in which a generic substrate, S is converted to two (2) products with equal molecular weight, PI and PII typical representation of hydrolysis of disaccharides. Scheme 5 presents the proposal such model.
  • 7. André Rosa Martins Int. Journal of Engineering Research and Applications www.ijera.com ISSN : 2248-9622, Vol. 4, Issue 11(Version - 5), November 2014, pp.101-112 www.ijera.com 107 | P a g e In this proposal, it is both formed a reaction complex with the substrate (ES) as a complex with one of the products (EPI) also, the representation of inhibition complex (EI). Scheme 5 - Proposed model for the inhibition of enzymatic hydrolysis of disaccharides I II k k k E  SES EP  P    1 2 1 (A) I k k I EP E  P    3 3 (B) I II k k k k I II EP P EI E P P ii ii i i            (C) In the Scheme 5 the stage (A) is the initial reaction, according to Michaelis-Menten kinetic. The stage (B) represented the hydrolysis process and the stage (C) represented the inhibition process. The proposed model assumes the mechanism of inhibition by the product to express the catalysis stage, asserting that inhibition effect occurs on the reaction complex (ES) forming a complex of inhibition (EI). The complex of inhibition is related to the free enzyme (E), with enzyme-product complex (EPI) and with the hydrolysis products (PI and PII), respecting the stoichiometry of the reaction. This is a competitive type of inhibition, by both reaction products and uncompetitive inhibition by reaction product that has no affinity to form a complex with the enzyme (in this case PII). Thus, the model designs a nonlinear system with seven (7) ordinary differential equations and nine (9) kinetic constants. Figure 5 shows the numerical results for the generic process. Figure 5 Response of the generic process for the enzymatic hydrolysis of disaccharides   I I ii ii I II k ES k E S k EP k E P k EI k E P P dt dE              ( ) ( ) 1 1 3 3 (29) ( ) ( ) 2 3 I 3 I i i I II I k ES k E P k EP k EI k EP P dt dEP          (30)
  • 8. André Rosa Martins Int. Journal of Engineering Research and Applications www.ijera.com ISSN : 2248-9622, Vol. 4, Issue 11(Version - 5), November 2014, pp.101-112 www.ijera.com 108 | P a g e k E S k ES k ES dt dES 1 1 2  (  )    (31) k E P P k EI k EP P k EI dt dEI ii I II ii i I II i         ( ) ( ) (32) ( ) 1 1 k ES k E S dt dS     (33) ( ) 0,5 0,5 ( ) 3 I 3 I ii ii I II I k EP k E P k EI k E P P dt dP            (34) 0,5 0,5 ( ) ( ) 2 ii ii I II i i I II II k ES k EI k E P P k EI k EP P dt dP             (35) The Figure 5b presents the expected behavior for a reaction process in which a substrate is divided into two products of equal molecular mass. At the beginning of the reaction there is a fluctuation, showing a concentration of PII slightly higher than the PI but throughout the process was observed a tendency of obtaining approximate concentrations of both products. Figure 5a shows the trend of increasing complex of inhibition and the consequent reduction of the reaction complex, with an initial fluctuation of the enzyme-product complex. This fluctuation on enzyme-product complex variation is associated, apparently, to the difference in the initial fluctuation of products concentration in the graph (Figure 5b). IV. RESULTS AND DISCUSSION The conservation of mass of the model (CMM) - throughout the process - was calculated according the following expression, where yi is the value of each carbohydrate concentration overtime and V is the different carbohydrate in the system. The value of the error - at the end of the process (Ef) - for not being linked to the enzyme substrate ratio (ESR) was calculated by comparing the numerical value of the initial substrate (S0) with the conservation of mass at the endpoint of the process. ( ) 1   V i i CMM y ; ( ( 1)) 1 0     V i f i E S y n (36) Figure 6 shows the result for the model proposal in this work only to substrate and products variation. Figure 6 - Response for variation of substrate and products
  • 9. André Rosa Martins Int. Journal of Engineering Research and Applications www.ijera.com ISSN : 2248-9622, Vol. 4, Issue 11(Version - 5), November 2014, pp.101-112 www.ijera.com 109 | P a g e Figure 7 - Response of hydrolysis of disaccharides with increment in time Figure 7 shows the result, for the model designed in this work, when the numerical value of the process time is increased ten times, maintaining other parameters equal to those in Figure 6. Additionally, it is observed that the sum of carbohydrate, at the end of the process in Figure 7, have a significantly lower error compared to the results obtained in the error of Figure 6. In order to check the error associated with the proposed model, and view the initial fluctuation in concentration of product, Figure 6 and Figure 7 shows the result only by changing the carbohydrate along the generic process, keeping the enzyme substrate ratio (ESR) equal to 0.1 (S = 100 and E = 10). Thus, it is possible to observe that the error, calculated at the end of the process, was 2.6122 and 0.3963, respectively to Figure 6 and Figure 7, and therefore, not related to the percentage ratio of enzyme-substrate, such as the inhibition presented by Johnson [12]. In the graph of Figure 7, it is seen a trend for error decay overtime, which allows us to infer the existence of a set of numerical values for the kinetic constants, which provide an error close to zero in a given process time. Thus, the situation indicates that the model, despite a proposal of product inhibition, differs from the behavior observed in Johnson [12], which was designed to represent the process of hydrolysis of sucrose disaccharides. Figure 8 shows the numerical results for the generic process S = 100, E = 10 and t = 20, foreseeing the conservation of mass of carbohydrates at the end of process. This response is shown the result with complete substrate conversion, keeping the same process time conditions and concentrations of substrate and enzyme shown in Figure 6. The numerical values of the kinetic constants, in Figure 8, were k1 = 165, k2 = k-1 = 70, other constants with numerical values equal to ten (10). The response, in Figure 8, shows - for the reaction products, the theoretical behavior expected for such enzymatic processes, with first order catalysis - kinetics in the beginning of the process, and at the end of the process, zero-order, i.e., it can be described (the reaction velocity) (v) as: dt dP dt dS v    → dt dP dt dP dt dS v I II     (37) Thus, it can be described as follow:  ( ) ( ) ( ) ( ) 1 1 3 I 3 I 2 ii ii I II i i I II  k ES  k E  S  k EP  k E  P  k ES  k EI  k E  P  P  k EI  k EP  P     k E S k E P k EP k EP P k E P P k k EI  k k ES I I i I II ii I II i ii ( ) ( ) ( ) ( ) ( ) 1 1 3 3 1 2                  (38)
  • 10. André Rosa Martins Int. Journal of Engineering Research and Applications www.ijera.com ISSN : 2248-9622, Vol. 4, Issue 11(Version - 5), November 2014, pp.101-112 www.ijera.com 110 | P a g e The Michaelis-Menten constant ( M k ), widely known, was applied to the equation ES: 1 1 2 k k k kM    (39) k E P k EP k EP P k E P P k k EI  k k k E S ES I I i I II ii I II i ii M ( ) ( ) ( ) ( ) ( ) 1 3 3 1 2                  (40) Hereafter, is postulated the existence of one kinetic constant for hydrolysis (kH) in step, assuming equal numerical values for the rate of this process stage, and also a single constant in the inhibition stage (kI) assuming equal constant numerical values for the effect of inhibition as follows: h k  k  k 3 3 → h H k k k k 1 2    (41) i i ii ii in k  k  k  k  k   → in I k k k k 1 2    (42) By applying the expressions of the hydrolysis and inhibition constant, in the equation representing ES, we have:     I I II I II H I I M k EP P E P P EI k E P EP k E S ES ( ) ( ) (  )  (   )  2       (43) Figure 8 - Response for hydrolysis of disaccharides with full conversion Finally, it was assessed if the model is sufficiently robust to the situation in which both enzyme substrate ratio (ESR) and process time are modified. Thus, the example of enzymatic hydrolysis of sucrose by invertase, originally studied by Michaelis and Menten is considered. Scheme 6 shows the model for the reaction shown in Figure 9, assuming that there is affinity of the enzyme to form a complex with glucose exclusively. Figure 9 shows the response to the process condition in which the numerical value of the substrate concentration was equal to 50 and the numerical value of the concentration of the enzyme was equal to 0.42. The numerical value of the process time was equal to 330.
  • 11. André Rosa Martins Int. Journal of Engineering Research and Applications www.ijera.com ISSN : 2248-9622, Vol. 4, Issue 11(Version - 5), November 2014, pp.101-112 www.ijera.com 111 | P a g e Scheme 6 - Proposed model for the inhibition of enzymatic hydrolysis of sucrose E S ES EG F k k k        1 2 1 (Initial stage of reaction) EG E G k k      3 3 (Hydrolysis stage) EG F EI E G F ii ii i i k k k k            (Inhibition stage) Figure 9 - Response of enzymatic hydrolysis of sucrose Figure 9 shows the response to the process condition in which the numerical value of the substrate concentration was equal to 50 and the numerical value of the concentration of the enzyme was equal to 0.42. The numerical value of the process time was equal to 330. In this model, the inhibition effect occurs from the increased concentrations of the products, competitive inhibition for glucose and fructose and uncompetitive inhibition for fructose. The enzyme substrate ratio (ESR) was equal to 0.0084, considering that, in previous ratios, was 0.1. Numerical values of the kinetic constants, for the adjustment shown in Figure 9 are: k1 = 5.50; k-1 = 5.32; k2 = 3.87; k3 = k-3 = 1.06; and ki = k-i = kii = k-ii = 50. The response on Figure 9 shows that reducing the amount of enzyme-substrate ratio (ESR) it tends to minimize fluctuations previously observed at the initial stage of products reaction, as regards the behavior of the model in this model. For Scheme 6, the equation representing variation of the complex reaction is shown as:     M H I k EG F E G F EI k E G EG k E S ES ( ) ( ) (  )  (   )  2       (44)
  • 12. André Rosa Martins Int. Journal of Engineering Research and Applications www.ijera.com ISSN : 2248-9622, Vol. 4, Issue 11(Version - 5), November 2014, pp.101-112 www.ijera.com 112 | P a g e Also, numerical values for the adjustment shown in Figure 9, in relation to the kinetic constants of hydrolysis of inhibition by Michaelis-Menten were: kM = 1.67; kH = 8.67 and kI = 0.18. V. CONCLUSION In this work, the inhibition stage of enzymatic reaction, represented by Michaelis-Menten kinetics, had its behavior described, by applying the proposed inhibition - increasing the concentration of the product in numerical solution of a generic process. The new model was applied on the enzymatic process that generated two (2) reaction products, both with equal molecular mass - in the case of hydrolysis of disaccharides. Unlike the current models which present inhibition by product, and provide an error linked to the percentage of the enzyme-substrate fraction; the aim of this work, combining competitive and uncompetitive inhibition, was allow to reach a result that minimizes the percentage error, and could provide conservation of mass to the sum of the substrate and products - after proper adjustment of the numerical values of the kinetic constants. Moreover, the model was robust concerning the variation ratio of the enzyme-substrate, also during the time process variation. Concluding, application of this approach - inhibition effect in the construction of new models - should be differentiated and applied to each specific situation, especially in cases of enzymatic catalysis that generate different reaction products. REFERENCES [1] K.A. Johnson; R.S. Goody, The original Michaelis constant: translation of the 1913 Michaelis-Menten paper. Biochemistry, v. 50, 2011, p. 8264-8269. [2] S. Chaudhury; O.A. Igoshin, Dynamic disorder in quasi-equilibrium enzymatic systems. PLoS ONE, v. 8, 2010, e12364. [3] IUB - International Union of Biochemistry. Symbolism and terminology in enzyme kinetics. Recommendations 1981. European Journal of Biochemistry, v. 128, 1982, p. 281-291. [4] D. Fange; M. Lovmar; M.Y. Pavlov; M. Ehrenberg, Identification of enzyme inhibitory mechanisms from steady-state kinetics. Biochimie, v. 93, 2011, p. 1623- 1629. [5] A.R. Tzafriri; E.R. Edelman, Quasi-steady state kinetics at enzyme and substrate concentrations in excess of the Michaelis- Menten constant. Journal of Theoretical Biology, v. 245, 2007, p. 737-748. [6] I. Stoleriu; F.A. Davidson; J.L. Liu, Quasi- steady state assumptions for non-isolated enzyme-catalysed reactions. Journal of Mathematics Biology, v. 48, 2004, p. 82-104. [7] M.I. Recht; F.E. Torres; D.D. Bruyker; A.G. Bell; M. Klumpp; R.H. Bruce, Measurement of enzyme kinetics and inhibitor constants using enthalpy arrays. Analytical Biochemistry, v. 388, 2009, p. 204-212. [8] E. Bakalis; M. Kosmas; E.M Papamichael, Perturbation theory in the catalytic rate constant of the Henry-Michaelis-Menten enzymatic reaction. Bulletin of Mathematical Biology, v. 74, 2012, p. 2535-2546. [9] J. Botts; M. Morales, Analytical description of the effects of modifiers and of enzyme multivalency upon the steady state catalyzed reaction rate. Transactions of the Faraday Society, v. 49, 1953, p. 696-707. [10] P. Schenker; A. Baici, Simultaneous interaction of enzymes with two modifiers: reappraisal of kinetic models and new paradigms. Journal of Theoretical Biology, v. 261, 2009, p. 318-329. [11] M.A.J.S. van Boekel, Kinetic modeling of reaction in foods. New York (USA): CRC Press, 2009. 788p. [12] K.A. Johnson, Review: A century of enzyme kinetic analysis, 1913 to 2013. FEBS Letters, v. 587, 2013, p. 2753-2766.