Aminotransferase enzymes catalyze which reaction?

• A. Exchange of amino groups and sulfhydryl groups between alpha-amino and sulfur-containing acids
• B. Exchange of amino and keto groups between alpha-amino and alpha-keto acids
• C. Hydrolysis of amino acids and keto acids
• D. Reversible transfer of hydrogen from amino acids to a coenzyme

Answer: (B)

Aminotransferase enzymes perform transamination, transferring the amino group from an amino acid to an alpha-keto acid. This exchange creates a new pair of amino and keto acids and is reversible, allowing amino groups to be shuttled between substrates as needed. The reaction is facilitated by pyridoxal phosphate (from vitamin B6) as a coenzyme. For example, alanine donates its amino group to alpha-ketoglutarate to form pyruvate and glutamate. This distinguishes aminotransferases from enzymes that hydrolyze amino acids or from those that transfer hydrogens to a coenzyme; the key action here is the transfer of an amino group between an alpha-amino acid and an alpha-keto acid.