energitics , kinetics of psychrophilic enzyme

1. PSYCHROPHILIC
ENZYMES

2. INTRODUCTION
PSYCROPHILES : PSYCRO-COLD, PHILIC-LOVING.
They thrive permanently at near zero
temperatures and synthesize cold active enzymes
to sustain life.
HABITAT: Oceans(-1 to +5degree celcius), polar
regions, alpines,The Himalayas,The Rocky
mountains and Alps.
They include large range of representatives from
all the three domains: Bacteria, Archea and
Eukarya.

3. INTRODUCTION
 Polar fish thriving beneath the icepack is the
biggest known psycrophiles.
 CHALLENGES:
 Low temperature,
 low liquid water availability,
 Lowered enzyme reaction and solute uptake rtae,
 Reduced membrane fluidity,

4. KINETICS OF PSYCHROPHILIOC ENZYMES
Usually at low temperature , the rate of the
enzyme catalysed rxn is low and there is slow
down of the molecular movements associated with
protein function.
Catalytic constsnt, Kcat : max. no. of substrate
molecules converted to product /active site/unit
time.

5. KINETICS
 The temperature dependence of the catalytic rate
constant is given by the relation;
EQN1--->1=
 where,k=transmission coefficient(generally close
to 1) kB =Boltzmann constant,h=Planck's
constant, R=universal gas constant.
 =the free energy of activation or the variation
of the Gibb's energy between ES*comp& ES.

6. KINETICS
Temperature dependence of activity. The activity of psychrophilic (open symbols, blue lines)
and mesophilic (closed symbols) enzymes recorded at various temperatures illustrates the
main properties of cold-adapted enzymes: cold activity and heat lability.

7. KINETICS
Indeed high activity at low temp. seems to arise
from increased flexibility of the protein structure .
The consequences of the improved mobility of the
protein structure is a weak stability.
As a result of such better accesibility, cold active
enzumes can accomodate substrates at lower
energy cost.

8. ENERGITICS OF COLD ACTIVITY
Reaction profile for an enzyme-catalyzed reaction with Gibbs energy changes under saturating
substrate concentration. Weak substrate binding (in blue) decreases the activation energy (
psychro) and thereby increases the reaction rate.

9. ENERGITICS
 Acc., to transition state theory; when the enzyme
encounters its substrate, the ES comp. falls into
an energy pit(potential barrier) i.e.,it reaches
transition state.
 For a rxn to proceed, activated ES# has to be
reached, then eventually breaks to E+P.
 Lower the G# , higher is the activity.

10. ENERGITICS
Cold active enzymes have a weak affinity for the
substrate=> energy pit is less deep.
Overall, magnitude of the energy pit is inversly
proportional to the activity.
In terms of ∆H# (activation enthalpy),the decrease
in the ∆H# enzymatic rxn of these enzymes is
considered as the main adaptive character to low
temperature.