Question

Which vitamin-derived coenzyme is required for a transamination reaction?

• A. Thiamine (Vitamin B1)
• B. Pyridoxine (Vitamin B6)
• C. FAD (Riboflavin / Vitamin B2)
• D. NAD (Niacin / Vitamin B3)

Hint:

The coenzyme that forms a Schiff base with amino acids is pyridoxal phosphate.

Answer 1

The Correct Option is B

Step 1: Define transamination.
Transamination is the transfer of an amino group (-NH₂) from an amino acid to an alpha-keto acid (usually alpha-ketoglutarate), generating a new amino acid (glutamate) and a new keto acid. It is catalysed by aminotransferases (transaminases) such as ALT and AST.

Step 2: Identify the coenzyme.
All transaminases use pyridoxal phosphate (PLP), the active coenzyme form of pyridoxine (Vitamin B6). PLP forms a Schiff base (aldimine) with the amino acid and shuttles the amino group via a pyridoxamine intermediate.

Step 3: Why the other options are wrong.
• Thiamine (B1) to thiamine pyrophosphate is needed for oxidative decarboxylation (pyruvate/alpha-ketoglutarate dehydrogenase, transketolase), not transamination.
• FAD (B2) to a hydrogen carrier in oxidation-reduction reactions (e.g. succinate dehydrogenase).
• NAD (B3) to a hydride acceptor in dehydrogenase reactions, not amino-group transfer.

Key fact: Transamination requires pyridoxal phosphate, derived from Vitamin B6 (pyridoxine).