1. Metabolism of Amino Acid

2. Amino Acid Pool 1. Dietary protein
The amount of free amino acids distributed throughout the body is called amino acid pool
Plasma level for most amino acids varies widely throughout the day . It ranges between 4-8 mg/ dl
It tends to increase in the fed state and tends to decrease in the post absorptive state
Sources of Amino acid pool
1. Dietary protein
2. Breakdown of tissue protein
3. Biosynthesis of nonessential amino acids

3. Fate of Amino acid pool
Biosynthesis of structural proteins. eg - tissue protiens
Biosynthesis of functional proteins. eg- haemoglobin, myoglobin etc.
Biosynthesis of small peptides of biological importance. eg- glutathione, endorphins
4. Biosynthesis of non protein nitrogens (NPN) as urea, uric acid, creatine , creatinine and ammonia
5. Catabolism of amino acids to give ammonia and α-keto acids

5. OVERVIEW OF AMINO ACID METABOLISM
ENVIRONMENT ORGANISM
Ingested
protein
Bio-
synthesis
Protein
AMINO
ACIDS
Nitrogen
Carbon
skeletons
Urea
Degradation
(required) 1 2 3 a b
Purines
Pyrimidines
Porphyrins c
Used for
energy
pyruvate
α-ketoglutarate
succinyl-CoA
fumarate
oxaloacetate
acetoacetate
acetyl CoA
(glucogenic)
(ketogenic)

6. Energy production from Amino Acids
GLUCOGENIC AMINO ACIDS –
Carbon skeleton can be converted to glucose
TCA cycle intermediates or pyruvate (gluconeogensis)
KETOGENIC AMINO ACIDS -
Carbon skeleton can be converted to ketone bodies

7. GLUCOGENIC / KETOGENIC AMINO ACIDS

10. Urea Cycle
Most animals convert excess nitrogen to urea, prior to excreting it. Urea is less toxic than ammonia.
The Urea Cycle occurs mainly in liver.
The 2 nitrogen atoms of urea enter the Urea Cycle as NH3 (produced mainly via Glutamate Dehydrogenase) and as the amino N of aspartate.
The NH3 and HCO3- (carbonyl C) that will be part of urea are incorporated first into carbamoyl phosphate.

11. Function: detoxification of ammonia (prevents hyperammonemia)
UREA CYCLE
mitochondria
cytosol
Function: detoxification of ammonia (prevents hyperammonemia)

12. Catabolic pathways of Amino acids
Transamination
Deamination
Transamidination
Transamidation
Decarboxylation

13. Transamination
Transamination means transfer of amino group from α-amino acid and a new α-keto acid with formation of a new α-amino acid and a new α-keto acid .
Liver is the main site of transamination
All amino acids can be transaminated except lysine , threonine, proline and hydroxyproline.
All transamination reactions are reversible
It is catalyzed by aminotransfereses. It needs pyridoxal phosphate as a coenzyme.

14. Transamination Examples of transaminase Alanine transaminase
Aspartate transaminase
Glutamate transaminase

15. Deamination
Deamination means the removal of amino group from α- amino acid in the form of amonia with the formation of α- keto acid
The liver and kidney are the main sites for deamination
Deamination may be oxidative or non-oxidative

16. Oxidative deamination
Glutamate Dehydrogenase catalyzes a major reaction that effects net removal of N from the amino acid pool.
It is one of the few enzymes that can use NAD+ or NADP+ as e- acceptor.

17. Some other pathways for deamination of amino acids:
1. Serine Dehydratase catalyzes:
serine  pyruvate + NH4+
2. Peroxisomal L- and D-amino acid oxidases catalyze:
amino acid + FAD + H2O 
a-keto acid + NH4+ + FADH2
FADH2 + O2  FAD + H2O2
Catalase catalyzes: 2 H2O2  2 H2O + O2