protein metabolism

1. PROTEIN
METABOLISM
Dr. ROOPA R
ASSISTANT PROFESSOR OF
BIOCHEMISTRY
GOVT. VELLORE MEDICAL COLLEGE &

2. PROTEIN METABOLISM
•Proteins are degraded in to
amino acids.
•Hence it is also considered to
be amino acid metabolism.

3. The 20 common amino acids of proteins

4. METABOLIC RELATION OF AMINO ACIDS
BODY PROTEINS
Proteosynthesis Degradation
AMINO ACIDS
DIETARY
PROTEINS
GLYCOLYSIS
KREBS CYCLE
NONPROTEIN
DERIVATIVES
Porphyrins
Purines
Pyrimidines
Neurotransmitters
Hormones
Komplex lipids
Aminosugars
UREA NH3
Conversion
(Carbon
skeleton)
250 – 300
g/day
ACETYL CoA
GLUCOSE CO2 KETONBODIES

5. PROTEIN METABOLISM
• First step in protein degradation is
removal of nitrogen atom in the form of
ammonia.
• Ammonia is converted into urea in most
of the mammals.
• Carbon skeletons are converted into
many important metabolic
intermediates.

6. Amino acid metabolism and
central metabolic pathways
20 amino acids are
converted to 7 products:
 pyruvate
 acetyl-CoA
 acetoacetate
 a-ketoglutarate
 succinyl-CoA
 oxaloacetate
 fumarate

7. C
O
R COO-
+ NH4
+
deamination
transamination
C
O
R COO-
CH
NH2
R COO-
CH
NH2
R COO-
oxidative
decarboxylation
CH2
NH3
+
R CO2
+
General reactions of amino acid catabolism

8. DE-AMINATION
• Oxidative- (Liver)
Glutamate ↔ α Ketoglutarate+NH4
Enz-glutamate Dehydrogenase
coenzyme-NAD+/NADP+
• By Amino Acid Oxidases
αAminoAcid→α-IminoAcid → α-Keto
Acid+NH4

9. Non Oxidative Deamination
• By AminoAcid Dehydratase;
Coenz-PLP
• Serine→Pyruvate+NH4
• Threonine→αKetobutyrate+NH4
• By Desulfhydrase; Cysteine

10. TRANSAMINATION
• Transfer of amino group of an
amino acid to a keto acid to form
a new amino acid and a new
Ketoacid
• PLP is coenzyme
• Most amino acids undergo
transamination except
Lysine,Threonine,Proline

11. TRANSAMINATION
1.Aspartate + α Ketoglutarate
AST
Oxaloacetate + α glutamate
2.Alanine + α Ketoglutarate
ALT
Pyruvate + α glutamate

12. Ammonia transport in the form of glutamine
Glutamine
synthetase
Excess ammonia is
added to glutamate
to form glutamine.
Glutamine enters the
liver and NH4
+ is
liberated in
mitochondria by the
enzyme glutaminase.
Ammonia is removed
by urea synthesis.

13. UREA CYCLE

14. Significance of Urea Cycle
• Disposal of Ammonia and Bicarbonate
• Generates the essential amino acid
arginine
• Ornithine gives rise to Proline and
Polyamines
• Integrates Nitrogen Metabolism to the
TCA cycle through Fumarate

15. Regulation of Urea Cycle
• By Feed Forward Mechanism-
depends on substrate
availability.
• Allosteric regulation – by NAG.
• Compartmentalization.

16. Energetics of Urea Cycle
• 2 ATP to make Carbamoyl
Phosphate.
• 1 ATP to make Argininosuccinate
which is equivalent to 2 ATP.
• TOTAL 4 ATP.

17. Enzyme defect Disorder
CPS -1 Hyperammonemia – 1
OTC Hyperammonemia – 2
Arginosuccinate
synthase
Citrullinemia
Argininosuccinate
lyase
Argininosuccinate
aciduria
Arginase argininemia
Disorders of Urea Cycle

18. THANK YOU