Step 1: What is transamination?
Transamination is the transfer of an amino group (-NH₂) from an amino acid to a keto acid, producing a new amino acid and a new keto acid. This is the central reaction of amino acid metabolism.
Step 2: What enzyme catalyses transamination?
Aminotransferases (transaminases) catalyse this reaction. Examples are ALT (alanine aminotransferase) and AST (aspartate aminotransferase).
Step 3: The required coenzyme.
All transaminases require Pyridoxal Phosphate (PLP), the active form of Vitamin B₆, as a coenzyme. PLP acts as an intermediate amino group carrier. It accepts the amino group from the donor amino acid (forming pyridoxamine phosphate) and then transfers it to the acceptor keto acid.
Step 4: Why are other options wrong?
Coenzyme Q (ubiquinone) is an electron carrier in the mitochondrial respiratory chain. NAD and FAD are coenzymes for oxidation-reduction reactions (dehydrogenases), not for aminotransfer.
Step 5: Conclude.
PLP is tightly and specifically linked to all transamination reactions in amino acid metabolism.
Answer: Option (4) — Pyridoxal Phosphate (PLP)