7 min readPathway sheetOften a 5-mark answer; 10 marks when asked together

Transamination and oxidative deamination

Transamination moves an amino group to a keto acid using vitamin B6 (PLP); oxidative deamination by glutamate dehydrogenase then releases it as free ammonia.

WhereMainly liver; GDH in mitochondria

Key enzymesALT, AST, glutamate dehydrogenase

CoenzymesPLP (B6) for transaminases; NAD⁺/NADP⁺ for GDH

End resultAmino N → glutamate → NH₃ → urea cycle

Transamination in two half-reactions

A keto acid is the carbon skeleton left when an amino acid loses its amino group. Transaminases (aminotransferases) pass the amino group from an amino acid to a keto acid. No free ammonia is released, and the reaction is reversible.

1★
Amino acid + enzyme-PLP → keto acid + enzyme-PMP
Aminotransferase (transaminase) · amino group held on the coenzyme as pyridoxamine phosphate (PMP)
2
α-Ketoglutarate + enzyme-PMP → glutamate + enzyme-PLP
Same aminotransferase · α-ketoglutarate is the usual acceptor, so nitrogen collects on glutamate

★ one-way, controls the pace

Two transaminases to know

Enzyme	Reaction	Clinical value
ALT, alanine transaminase (old name SGPT)	Alanine + α-ketoglutarate ⇌ pyruvate + glutamate	Mostly in liver, so a raised level points to liver cell damage (hepatitis, fatty liver)
AST, aspartate transaminase (old name SGOT)	Aspartate + α-ketoglutarate ⇌ oxaloacetate + glutamate	In liver, heart and muscle; rises in liver disease and after a heart attack (myocardial infarction)

Oxidative deamination and transdeamination

Deamination removes the amino group as free ammonia (NH₃). Glutamate is the main amino acid deaminated, in liver mitochondria. Transamination followed by deamination of glutamate is called transdeamination.

1
Amino acid + α-ketoglutarate → keto acid + glutamate
Aminotransferases (PLP) · collects nitrogen from most amino acids
2★
Glutamate + NAD⁺ (or NADP⁺) + H₂O ⇌ α-ketoglutarate + NH₃ + NADH (or NADPH)
Glutamate dehydrogenase (GDH) · liver mitochondria · reversible · ATP and GTP inhibit; ADP and GDP activate
3
NH₃ + CO₂ → carbamoyl phosphate
Carbamoyl phosphate synthetase I · ammonia enters the urea cycle

★ one-way, controls the pace

Transamination vs oxidative deamination

TransaminationMoves the amino group to a keto acid. No free ammonia. Needs PLP (vitamin B6). Reversible, so it also helps make non-essential amino acids. All amino acids take part except lysine and threonine (some books, e.g., Satyanarayana, also exclude proline and hydroxyproline).

Oxidative deaminationRemoves the amino group as free NH₃. Mainly glutamate, by glutamate dehydrogenase, using NAD⁺ or NADP⁺ (from niacin). Happens in liver mitochondria, close to where the urea cycle starts.

A minor route: L- and D-amino acid oxidases (flavoproteins using FMN and FAD) also deaminate amino acids, but they matter little.

Nutrition link

Every transaminase needs pyridoxal phosphate (PLP), the active form of vitamin B6. Whole cereals, pulses, nuts, meat and fish supply it. GDH uses NAD⁺/NADP⁺, made from niacin (B3). Blood ALT and AST are part of the liver function test, which a dietitian reads in hepatitis, fatty liver and alcoholic liver disease.

Exam angle

2 marks: “What is transamination? Give an example.” Transfer of an amino group from an amino acid to a keto acid by a PLP-dependent transaminase, e.g., alanine + α-ketoglutarate ⇌ pyruvate + glutamate (ALT).

5 marks: “Write a note on oxidative deamination.” GDH in liver mitochondria turns glutamate into α-ketoglutarate and NH₃ using NAD⁺/NADP⁺; add its regulation and transdeamination.

10 marks: “Describe transamination and deamination of amino acids with their significance.” PLP half-reactions, ALT and AST examples, the GDH reaction, a transdeamination diagram, ALT/AST as liver markers and the B6 link.

Remember it

SGPT = ALT: the P is for pyruvate, made from alanine. SGOT = AST: the O is for oxaloacetate, made from aspartate.