Which coenzyme is required for AST and ALT transaminase reactions?

• A. Pyridoxal phosphate (Vitamin B6)
• B. NAD+
• C. FAD
• D. Coenzyme A

Answer: (A)

The essential cofactor for aminotransferase reactions is pyridoxal phosphate, the active form of vitamin B6. PLP acts as a temporary carrier for the amino group, enabling the transfer from an amino acid to an α-keto acid through Schiff base chemistry. In alanine aminotransferase, the amino group from an amino acid is transferred to pyruvate to form alanine, while α-ketoglutarate becomes glutamate. In aspartate aminotransferase, the amino group is transferred to oxaloacetate to form aspartate, with α-ketoglutarate again becoming glutamate. This cycling of PLP between forms allows the amino group to move between substrates efficiently. The other cofactors listed (NAD+, FAD, CoA) are involved in redox or acyl-transfer reactions, not transamination, so they are not required for ALT/AST activity.