metabolism of proteins and amino acids, ammonia metabolism, urea cycle,transamination and deamination.

2. Protein & Amino acid
Metabolism
Dr.Ganesh

3. Protein and Amino acid Metabolism
The syllabus for this chapter includes
the following topics.
PART I

4. Protein and Amino acid Metabolism
Breakdown of tissue proteins and amino
acid pool, General Reactions of Amino
acids.
Disposal of Ammonia: urea cycle,
glutamate and glutamine formation.
Metabolism of Amino acids,- Glycine,
serine

5. Introduction
Overview of Amino Acid
Metabolism
Nitrogen Balance and amino acid
pool
Protein Turnover
Metabolism of Amino Nitrogen
Metabolism of Individual Amino
Acids – Glycine and serine

6. Protein and Amino acid Metabolism
PART II
Metabolism of Amino acids
sulfur containing amino
acids, aromatic amino acids,
histidine & arginine

7. Introduction
Proteins are linear hetero polymers
of α – L – Amino acids, which are
linked by peptide bonds. Nitrogen
(N) is characteristic of proteins.
Amino acids are not stored by the
body. Hence, they must be obtained
from the diet, synthesized de novo,
or produced from normal protein
degradation.
Any amino acids in excess of the
biosynthetic needs of the cell are
rapidly degraded.

8. Biological importance:
1.Proteins contain nitrogen and they
are main source of nitrogen for the
body. Dietary Proteins are the
sources of essential amino acids for
the body.
2.All amino acids are required for the
synthesis of proteins and many amino
acids serve as precursors for the synthesis
of biologically important compounds (Eg:
Melanin, serotonin, creatine etc.)

9. Medical importance:
1.Genetic defects in the pathways of
amino acid metabolism can cause serious
disease. Eg: Albinism,
Phenlyketonuria, Alkaptonuria
etc.
2. Dietary deficiancy of proteins can
result in disease such as P.E.M
(protein energy malnutrition)

10. NITROGEN BALANCE
Nitrogen balance = Difference between
total nitrogen intake and total nitrogen loss
from the body.
The normal adult is in nitrogen equilibrium,
nitrogen intake = nitrogen output.

11. Amino acid catabolism- phases
1.The first phase of catabolism involves the
removal of the α – amino groups (usually by
transamination and subsequent deamination)
ammonia
+
corresponding α – Keto
Converted to UREA
acid.
Enters 2nd phase
and excreted.
(most important route for disposing of nitrogen
from the body.)

12. Amino acid catabolism- phases
2. 2nd phase of amino acid
catabolism
the carbon skeleton of the α – Ketoacids
via intermediates of energy
producing, metabolic
pathways
CO2 + H2O, glucose, fatty acids, or
ketone bodies

Non essential amino acids are synthesized
from the intermediates of metabolism or from
essential amino acids

13. Amino acid pool
Amino acids
released by
hydrolysis of dietary
or tissue protein or
synthesized de
novo, and are
distributed
throughout the
body.
Collectively,
they constitute
the amino acid
pool.

14. BODY PROTEIN
DIATARY PROTEIN
Digestion and
absorption
Synthesis of
new amino
acids
catabolism
synthesis
AMINO ACID POOL
SYNTHESIS OF
BIOLOGICALLY IMP.
COMPOUNDS
CATABOLISM

15. PROTEIN TURNOVER:
the continuous degradation and resynthesis of all cellular
proteins
Each day about 1–2% of the total body proteins, principally
muscle protein, undergoes turnover.
Body proteins
Reutilization for
new protein
synthesis
degradation
Amino acids
Catabolism

16. Metabolism of Amino Nitrogen
Overview
Transamination
Deamination Reactions (Ammonia
Formation)
•Oxidative deamination
•Non-oxidative deamination
Ammonia Transport
Disposal of Ammonia – Urea cycle.

17. Overview of Metabolism of
Amino Nitrogen
-Ketoglutarate
Amino acids
Transmination
Glutamate
Keto acids
-NH2
Oxidative deamination
Aspartate
-NH2
CO2
Other
Reactions
NH3
Urea
Cycle
Urea
H2N-CO-NH2

18. TRANSAMINATION
Definition: Transamination is the transfer of
the amino group of an amino acid to a keto
acid, changing the latter into a new amino acid
and the original amino acid into a new keto
acid.
Transamination reaction is freely reversible and
hence involved both in biosynthesis and
catabolism of amino acids.
Enzyme Involved:“Transaminases”
(aminotransferases) – liver, skeletal muscles
and heart are particularly rich in
transaminases.
Cofactor Required: Pyridoxal phosphate
(PLP) derived from Vit B6 (pyridoxine).

19. General Reaction:
AMINO ACID 1
KETO ACID 1
PLP
TRANSAMINASE
KETO ACID 2
AMINO
ACID2

20. Mechanism:
 Pyridoxal phosphate is bound to the transaminase
at the catalytic site and during transamination the
bound coenzyme serves as a carrier of amino
groups.
Transamination occurs in 2 stages –
1.Transfer of the amino group of an amino acid to the
coenzyme PLP (bound to the enzyme) to form
pyridoxamine phosphate and the corresponding ketoacid.
2.The amino group of pyridoxamine phosphate is
then transferred to an -ketoacid to produce a new
amino acid and the enzyme with PLP is regenerated.

21. Examples:
1) Alanine
Ketoglutarate
2) Aspartate
ALT
PLP
AST
Pyruvate
Glutamate
Oxaloacetate
PLP
Ketoglutarate
Glutamate
ALT Alanine Transaminase; AST Aspartate transaminase

22. Salient features:
All amino acids except lysine, threonine,
proline and hydroxyproline undergo
transamination.
It is a reversible reaction and can serve in
both formation of an amino acid and its
catabolism.
For all transaminases, glutamate and
-Ketoglutarate are one pair of substrate ( an
amino acid and its corresponding keto acid)
and differ in the other pair.
The amino acids undergo transamination to
finally concentrate nitrogen in glutamate.

23. Metabolic Functions:
1.Diverting excess of amino acids
towards catabolism and energy
production with simultaneous
urea synthesis.
2.Biosynthesis of non-essential
amino acids.
3.Producing -keto acids (e.g.
oxaloacetate, Pyruvate, ketoglutarate) for subsequent
gluconeogenesis

24. Clinical Aspects:
Blood levels of ALT and AST
are elevated in liver diseases
and AST levels in myocardial
infarction. Their estimation is
useful in the diagnosis of
these conditions. (refer Enzymes)

25. Describe transamination.
Mention the clinical significance
of serum transaminases. (4)
Clinical importance of
transamination
(3) Questions??
Write the reaction, with
cofactors if any, catalyzed by
Alanine transaminase. (3)
Name the coenzyme forms of
vitamin B6; write the
mechanism of transamination

26. Ammonia Formation –
Deamination Reactions
Ammonia is Produced in the Body by:
1) Cellular Metabolism and
2) In the Intestinal Lumen.

27. 1.Ammonia formation by cellular
metabolism
Cells produce ammonia mostly from
amino acids by deamination, which may
be either
1. oxidative or
2. non-oxidative

28. Deamination Reactions(Ammonia
formation)
Deamination is removal of amino group
from compounds, mostly amino acids, as
ammonia (NH3).
NH3 +carbon skeleton of amino acid
(KETOACID)
CONVERTED TO
UREA

29. Deamination….2types
1.Oxidative deamination
a)deamination of glutamate catalyzed
by glutamate dehydrogenase.
-Most important
b)Other Oxidative Deamination Reactions
are Mainly Those:
-- Catalyzed by Amino Acid Oxidases
2.Non-Oxidative Deamination(less
important)
Enzymes Involved are:
Dehydratases
Lyases
and
Amide Hydrolases

30. Oxidative Deamination by
Glutamate Dehydrogenase
(GDH):
The removal of the amino group from
glutamate to release NH3 and -ketoglutarate
coupled with oxidation is known as oxidative
deamination
Site: Most active in mitochondria of liver
cells, though present in all cells.
Enzyme: Glutamate dehydrogenase (GDH) – a
Zn containing mitochondrial enzyme.
Coenzymes: NAD+ or NADP+

31. Oxidative deamination of glutamate…
+
NAD / NADP
+
Glutamate + H2O
NADH/ NADPH + H
+
-Ketoglutarate + NH3
Glutamate dehydrogenase (GDH)

32. Role of GDH:1. Produces NH3, thus channeling the amino
groups of most amino acids for urea
synthesis.
2. Regenerates -ketoglutarate for further
collection of amino groups of amino acids
by transamination and producing their
carbon skeletons.
3. NADH produced generates ATP in the
ETC.
4. The reverse reaction is required for the
biosynthesis of glutamate and in the
tissues for fixing ammonia, which is
toxic.

33. What Is Transdeamination ??
Transamination and
deamination often
occur simultaneously
involving glutamate as
the central molecule.
this process is called
transdeamination.

34. What Is Transdeamination ??
All amino acids
TISSUES
transamination
-KG
Keto acids
GLUTAMATE
Deamination in liver
NH3+ -KG
UREA
Carried by blood
Reaches
liver

35. Glutamate occupies a central position in the
metabolism of -amino nitrogen of -amino acids.
The -amino groups of most of the amino
acids ultimately are channeled/transferred to
-ketoglutarate by transamination, forming
glutamate
Glutamate channels the amino groups to form
urea (H2N–CO–NH2) in the liver.
By oxidative deamination the amino group in
glutamate may form ammonia, which forms
one of the –NH2 groups of urea.
By transamination glutamate can also pass its
amino group to oxaloacetate forming
aspartate, which donates its amino group to
form the other – NH group of urea.

36. What are the sources of ammonia in the
body?
Explain the biochemical basis: glutamate
plays a central role in the catabolism of
amino nitrogen of amino acids.

Give 2 examples for each of the
following.
a)Transaminases b) Reactions forming
ammonia
Write the reaction, with cofactors if any,
catalyzed by Glutamate dehydrogenase.

37. Oxidative Deamination by
Amino Acid Oxidases
• Amino Acid Oxidases are:
-- Flavoproteins
-- Possessing either FMN or FAD
Amino Acid
FAD/FMN
Amino Acid Oxidase
FADH2/FMNH2
-Keto Acid + NH3

38. Non-Oxidative Deamination
Enzymes Involved are:
Dehydratases
Lyases
and
Amide Hydrolases

39. Dehydratase
Amino Acid Dehydratases (PLP-dependent)
Serine/Threonine
Dehydratase
PLP
NH3
Pyruvate/ -Ketobutyrate

40. Amino Acid Lyase
Histidine
Aspartate
Histidase
Aspartase
NH3
NH3
Urocanate
Fumarate

41. Amino Acid Amide Hydrolases
Glutamine
Aspargine
H2O
H2O
Glutaminase
Asparginase
NH3
NH3
Glutamate
Aspartate

42. 2)NH3 production in intestine
Intestinal Lumen -- Another Major Source
of Ammonia
by the Action of Bacteria on:
-- Urea Present in the
Intestinal Juice
And
Dietary Amino Acids.
• This Ammonia is Absorbed into Hepatic
Vein and Enters Liver Directly.

43. Transport of Ammonia
Ammonia is toxic to tissues,
especially to brain (see Ammonia
Toxicity).
Ammonia that is constantly
produced in the tissues is
transported to liver for
detoxification by urea synthesis.
Ammonia is transported in blood
as 1) free NH3, as 2) glutamate
or as 3) glutamine.

44. Transport of Ammonia…
• NH3is transported in 3 forms.
1) As free NH3 Ammonia, whose blood level
is 10 to 80 gm/dl, is rapidly removed from
the circulation by the liver and converted to
urea.
2) as glutamate Inside the cells of almost all
tissues ammonia combines with Ketoglutarate to form glutamate by GDH
and is transported to the liver.

45. Transport of Ammonia…
3) as glutamine. Ammonia is also trapped
by glutamate in the tissues, especially in the
brain, to form glutamine, which is catalyzed
by glutamine synthetase
NH3
Glutamine synthetase
Glutamate
ATP
glutamine
.Mg2+
ADP+Pi
Transported to liver via blood

46. This reaction may be
considered as the first
line of detoxification of
NH3 in the brain.
Glutamine is then
transported through
circulation (highest blood
level among all amino
acids) to liver
In liver, this reaction is reversed
to release NH3 .

47. In the liver..
Glutaminase
Glutamine
H2O
glutamate
NH3
UREA

48. UREA CYCLE
(Detoxification of Ammonia)
Contents:
• Synonyms
• Site
• Sources of Atoms of Urea
• Reactions
• Functions
• Ammonia Toxicity – Hyperammonemia

49. UREA CYCLE .
(Detoxification of Ammonia)
• Ammonia is Toxic to the Body.
• Hence it is Necessary that the NH3
Produced During Metabolism of Amino
Acids be Removed Immediately.
• This is Done by Conversion of Toxic NH3
into Harmless Water-soluble Urea in the
Liver by Urea Cycle.

50. UREA CYCLE
(Detoxification of Ammonia)
• Synonyms:
Urea Cycle
Ornithine Cycle
Krebs-Henseleit Cycle
• Site:
Urea Synthesized in Liver
Carried by Blood
And
Excreted by Kidneys

51. Sources of Atoms of Urea
NH2
O
||
C
NH2
NH3
CO2
Aspartate

52. UREA CYCLE
(Detoxification of Ammonia)
• Urea Synthesis:
-- A 5-step Cyclic Process
• Enzymes of the First 2 Steps:
-- Present in Mitochondria
• While the Rest:
-- Located in the Cytosol

53. Reactions of Urea Cycle
CO2 + NH3 + 2 ATP
Carbamoyl Phosphate Synthetase–I (CPS-I)
Carbamoyl Phosphate + 2 ADP + Pi
Urea
Ornithine
Arginase
TCA cycle
Arginine
Ornithine Transcarbamoylase
Fumarate
Arginosuccinase
Citruline
Arginosuccinate
Aspartate
Arginosuccinate Synthetase
ATP
AMP + PPi

54. Functions of Urea Cycle
1.Detoxification of NH3
2.Biosynthesis of Arginine.

55. Ammonia Toxicity –
Hyperammonemia
• Ammonia Concentration Rises in the Blood
(Hyperammonemia) and in other Tissues in:
-- Liver Failure
and
-- Inborn Errors of Urea Synthesis
(that is, due to Genetic Defect)
• This Produces Ammonia Toxicity in Many
Ways.

56. Causes Of Hyperammonemia
• Causes may be
1.Acquired or 2. Inherited
1.Acquired Causes
– Liver Diseases (e.g. Cirrhosis and Severe
Hepatitis)
-- Liver is Unable to Convert Ammonia
into Urea
– -- Blood Ammonia Level Rises.

57. 2.Inherited Causes
-- Defects Associated with each of the
Enzymes of Urea Cycle Exist.
-- The Levels Substrate of the Defective
Enzyme
Rises in the Cells.
-- This Causes Product Inhibition of the
Enzyme
Catalyzing the Earlier Step.
-- Leading to Accumulation Ultimately of
the Starting Substrate,
Namely, NH3

58. Inherited Causes of Hyperammonemia
Disease
Hyperammonemia Type-I
Enzyme involved
CPS-I
Hyperammonemia Type –II
Ornithine
Transcarbamoylase
Citrullinemia
Argininosuccinate
Synthetase
Argininosuccinic Aciduria
Argininosuccinase
Hyperarginemia
Arginase

59. Ammonia Toxicity –
Hyperammonemia
• Biochemical Alterations:
– Hyperammonemia,
– In Blood of Intermediates Prior to Metabolic Block
– Urinary NH3
• Clinical Manifestations
Nausea, Vomiting, Protein Intolerance.
Slurring of Speech, Blurring of Vision
Tremor (Flapping Tremors), Ataxia, Lethargy
Mental Retardation (in the Inherited Hyperammonemia
in Children)
Dizziness, Coma, Death

60. Blood Urea
In Healthy People, Normal Blood Urea
Concentration is 12-36 mg/dL
Higher Protein Intake Marginally
Increases Blood Urea Level; however,
this will be within Normal Range.
(See Practical Manual for Clinical
Significance of Blood Urea)

61. 1. How ammonia is formed in the body? Explain
the reaction leading to the detoxification of
ammonia.
2. Describe the urea cycle. What is the normal
blood urea level? Name two conditions in which
blood urea level increases.
3. Explain the steps of Urea cycle & Mention the
names of its disorders.
4.Carbamoyl phosphate synthetase deficiency.
5.Give 2 examples for each of the following.
a) Causes for inherited disorders of urea cycle
b)Conditions in which blood urea level
increases

62. Metabolism of Glycine
H
H2N–C–COOH
H
R Group
GLYCINE is the simplest, optically inactive,
glucogenic and non-essential amino acid.

63. Metabolism of Glycinecontents
Synthesis
Catabolism
Synthesis of biologically imp. Compounds
from glycine
Inborn errors of glycine metabolism

64. Synthesis
Glycine is a non-essential amino
acid as it can be synthesized in
the body.
It can be synthesized from many
substances by separate
reactions.

65. • The major reactions are from:
1.Serine
2.CO2, NH3 and N5, N10 methylene
tetrahydrofolate (N5, N10 methylene
FH4)
3. And Glyoxylate
• These are reversible reactions and thus
also play a role in the catabolism of
glycine.
• Minor pathways for synthesis of
glycine are from:
Threonine and Choline

66. 1. Synthesis of Glycine from
Serine:
Serine hydroxy methyl transferase
COOH
COOH
PLP
HC-NH2
CH2OH
Serine
CH2
FH4
N5, N10-methylene FH4
NH2
Glycine
One carbon unit (methylene group, –CH2–) from
serine is transfered to tetrahydro folic
acid (FH4).

67. 2. Synthesis of Glycine from
CO2, NH3 and N5, N10 methylene
THFA:
• This reaction is catalyzed by glycine synthase.
COOH
NADH + H+
NAD+
CH2-NH2
GLYCINE
CO2 + NH3
N5, N10-methylene FH4
FH4

68. 3. Synthesis of Glycine from
Glyoxalate:
Glutamate
COOH
CHO
Glyoxylate
-Ketoglutarate
PLP
Transaminase
Glycine

69. 4. Synthesis of Glycine from
Threonine:
COOH
Threonine Aldolase
COOH
HC - NH2
H –C- OH
CH3
Threonine
CHO
+
CH2-NH2
Glycine
CH3
Acetaldehyde

70. Catabolism:
• There are several paths for catabolism of
glycine.
• All, except one, are reversals of
biosynthetic pathways.

71. 1. By the Action of Serine
Hydroxy Methyl Transferase:
-This is also utilized for the
synthesis of serine.
5 10
FH4
N , N methylene FH4
PLP
Glycine
Serine
Serine hydroxy methyl transferase
Pyruvate

72. 2. By the Action of Glycine
synthase ( also called Glycine
Cleavage System):
5 10
N , N methylene FH4
FH4
Glycine
CO2 + NH3
Glycine synthase
NAD
+
+
NADH+H

73. 3. Transamination:
- Ketoglutarate
Glutamate
PLP
Glycine
Glyoxylate Oxalate (excreted in urine)
Transaminase

74. Functions of Glycine:
1.Required for protein
synthesis.
2.It forms many biologically
important compounds – glucose,
serine (a non-essential amino acid),
heme, conjugated bile acids,
creatine, glutathione and purines
3.It provides its carbon atom
for one carbon pool.
4.It is required for certain
detoxification reactions.
4.It acts as a
neurotransmitter

75. Functions of
Glycine…..detoxification
Benzoic acid, a
food preservative,
is found in small
amounts in foods.
Glycine
Benzoic acid
CoA SH
Benzoyl CoA
It is detoxified in
the liver by
conjugation with
Glycine to form
water soluble,
Non-toxic
Hippuric acid.
Hippuric acid
CoA SH
Excreted in urine

76. Functions of Glycine….
Synthesis of biologically imp.
compounds
1. CONSTITUENT OF PROTEINS:
 Glycine is mainly present at the bending points
because of its small size.
 Collagen is the protein rich in Glycine; about 33% of
the amino acids is Glycine.
2. GLUCOGENIC ROLE
Glycine
Serine
Pyruvate
Glucose

77. Functions of Glycine….
3.SYNTHESIS OF SERINE
Serine hydroxy methyl transferase
Glycine
Serine

78. Functions of Glycine….
4. HEME BIOSYNTHESIS
Glycine is one of the starting materials
along with succinyl CoA for heme
biosynthesis.
Glycine + succinyl CoA
-Amino levulinic acid ( ALA) Heme
ALA synthase

79. Functions of Glycine….
5. SYNTHESIS OF CONJUGATED BILE
ACIDS:
Cholic acid
Glycine
Glycocholic acid
Conjugated
Bile Acids
Chenodeoxy cholic acid
Glycine
Glycochenodeoxy cholic acid.

80. Functions of Glycine….
5.CREATINE SYNTHESIS
Creatine phosphate is formed from
glycine, arginine and S-adenosyl
methionine (SAM), in kidneys and
liver.

81. Functions of Glycine….creatine synthesis
Glycine
Arginine
In Kidney
Ornithine
Guanidoacetate
S-adenosyl methionine (SAM)
In Liver
S-adenosyl homocysteine (SAH)
Creatine
ATP
Creatine
Phosphokinase (CPK)
ADP
Pi + H2O
Creatinine
Creatine phosphate
(NPN substance excreted Non-enzymatic (spontaneous)
In urine)

82. Function of Creatine
Phosphate:
Creatine phosphate occurs mainly in muscles.
It is a high-energy compound ( Go'= 10.5) and
storage form of energy in muscle.
During the resting phase in muscle (relaxed)
creatine is stored as creatine phosphate, which is
produced by phosphorylation of creatine by ATP.
Muscle needs ATP for contraction. During
prolonged muscle contraction
depletion
of ATP. During this period creatine phosphate
rephosphorylates ADP to ATP

83. In muscles……
During resting phase(*ATP stores are full)
ATP
Muscle creatine phosphokinase
ADP
(CPK)
CREATINE
CREATINE PHOSPHATE
During prolonged contraction
(*when ATP stores are depleted)

84. Functions of Glycine….
6.
SYNTHESIS OF GLUTATHIONE:
Glutathione ( -glutamyl-cysteinyl-glycine) is
a tripeptide formed from glycine, glutamate
and cysteine.
The reduced form is monomeric and carries
hydrogen atom in the sulfhydryl group(SH) of cysteinyl residue.
The oxidized form is dimeric.

85. GLUTATHIONE…..
– Glu – Cys – Gly
– Glu – Cys – Gly
SH
S
Reduced Glutathione (GSH)
S
– Glu – Cys – Gly
Oxidized Glutathione (GS–SG)

86. GLUTATHIONE SYNTHESIS:
Glutamic acid + Cysteine
ATP
ADP+Pi
- Glutamyl cysteine
Glycine
Glutathione

87. FUNCTIONS OF GLUTATHIONE:
1.It serves as an Anti- oxidant in the body.
2.It serves as a cofactor for certain enzymes, such
as glutathione peroxidase, which uses reduced
glutathione to detoxify hydrogen peroxide.
Eg : RBC membrane integrity is maintained due
to this action.
3.It is conjugated to drugs to make them more
water-soluble, so that, they can be easily excreted
..
4.It also plays a role in the transport of amino acids
across the plasma membrane in certain cells.

88. Functions of Glycine….
7. SYNTHESIS OF PURINE RING:
• C4, C5 and N7 of the purine ring are
provided by glycine.
• Thus the whole molecule of glycine is
involved in the synthesis of purine.
•

89. Inborn Errors of Glycine
Metabolism:
1.Glycinuria:
This is a rare genetic disorder, probably resulting
from a defect in the renal tubular reabsorption
of glycine.
It is characterized by excessive excretion of
glycine in urine (0.6 – 1 g per day) and a
tendency to form oxalate renal stones.
However, plasma glycine levels are normal.

90. 2.Primary Hyperoxaluria:
Genetic/metabolic defect:
failure to catabolize glyoxalate.
glyoxalate is oxidized to oxalate.
overproduction of
oxalate
excessive excretion of oxalate in
urine (hyperoxaluria).

91. progressive bilateral calcium renal
stones
nephrocalcinosis and frequent
urinary tract infection
hypertension and renal failure.

92. Proteins
Serine
GLYCINE
CO2 + NH3
Transamination
Urea
Threonine
Oxidation
Glyoxylate
Creatine
C4, C5, N7 of Purine ring
Heme
Glutathione
Bile salts
Conjugation
E.g. Hippuric acid

93. 1.Explain the metabolism of glycine. Mention two
disorders of glycine metabolism and their defects.
2.Enumerate the compounds formed from glycine,
giving their biochemical importance.
3.Why glycine is nutritionally non-essential?
4.Metabolic role of glycine.
5.Mention the compounds formed from Glycine.
6.How is Creatinine synthesized? Discuss about
creatinine clearance and its significance.
7.How creatine phosphate is synthesized. Mention
the significance of estimation of urinary
creatinine.
8.Glutathione and its functions.

94. Metabolism of Serine
H2N – CH – COOH
CH2
OH
Serine is an aliphatic hydroxy, nonessential and glucogenic amino acid.

95. Metabolism of Serine
H2N – CH – COOH
CH2
OH
Serine is an aliphatic hydroxy, nonessential and glucogenic amino
acid.

96. Metabolism of serine:
Synthesis:
Catabolism:
Functions:

97. Synthesis:
3-Phosphoglycerate(Glycolytic
intermediate)
(major source)
SERINE
serine hydroxy methyl transferase
Glycine

98. Functions of Serine:
1.Required for protein synthesis.
-As a constituent of protein it serves an important
role in esterifying the phosphate groups as prosthetic
group of proteins. Eg: casein
-Enzyme regulation by phosphorylation and
dephosphorylation
-Forms active site of a group of enzymes called as
serine proteases. Eg: trypsin
2.It provides its carbon atom for one carbon
pool (by serine hydroxy methyl transferase
reaction)

99. Functions of Serine….
3.It forms many biologically important
compounds
a)glucose,
b)non-essential
amino acids
• Serine is glucogenic
• cysteine, alanine and
glycine
• required for synthesis of
c) choline,
phospholipids and
ethanolamine
acetylcholine
d)sphingosine
• for synthesis of
sphingolipids.

100. SERINE-Clinical Aspects
Serine
analogues
inhibit
nucleotide
synthesis
So, they are used as
drugs e.g. azaserine
(anticancer drug)
cycloserine
(antitubercular drug)