SN1 SHORT NOTE 5M ★ High-yield

Define transamination. Describe its mechanism, significance and clinical applications.

Biochemistry · 1st Professional — Pre-Clinical

Definition

Transamination = the reversible transfer of an α-amino group from an amino acid to an α-keto acid, forming a new amino acid and a new keto acid.

Amino acid1 + Keto acid2 ↔ Keto acid1 + Amino acid2

Features

Enzyme — aminotransferase (transaminase)
Coenzyme — pyridoxal phosphate (vitamin B6) for every transaminase
Freely reversible; ΔG is near zero
No free ammonia is released and no nitrogen is lost — it is a redistribution, not an excretion
α-Ketoglutarate is the usual acceptor, so nitrogen is funnelled into glutamate
Occurs in cytosol and mitochondria of most tissues, especially liver and muscle

Amino Acids That Do Not Transaminate

Lysine, threonine, proline and hydroxyproline
All others do, including the essential ones — which is why their keto acid analogues can substitute for them in the diet

Mechanism — Ping Pong Bi Bi

PLP + amino acid → Schiff base (aldimine) → Tautomerisation → ketimine → Hydrolysis → Keto acid1 released; enzyme now carries pyridoxamine phosphate → Second keto acid binds → Reverse sequence → Amino acid2 released; PLP regenerated

Clinically Important Transaminases

Enzyme	Reaction	Normal	Raised in
ALT (SGPT)	Alanine + α-KG ↔ pyruvate + glutamate	7–40 U/L	Liver disease — more specific; very high in viral hepatitis
Ast (SGOT)	Aspartate + α-KG ↔ oxaloacetate + glutamate	10–40 U/L	Liver, myocardial infarction, muscle disease, haemolysis

CLINICAL PEARL

Ast : ALT ratio — above 2 suggests alcoholic liver disease (ast is also released from mitochondria and ALT synthesis needs B6, which alcoholics lack); below 1 suggests viral hepatitis or fatty liver.

Significance and Applied Aspects

Collects nitrogen from all amino acids into glutamate, the single substrate for oxidative deamination — the funnel principle
Allows synthesis of non-essential amino acids from available keto acids
Links amino acid metabolism to the TCA cycle through pyruvate, oxaloacetate and α-ketoglutarate
Diagnostic — the transaminases are among the most widely used enzymes in clinical medicine
Vitamin B6 deficiency impairs all transaminations; a transaminase assay with and without added PLP is used to assess B6 status

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