Schiff base
In KYNU reaction, PLP facilitates Cβ-Cγ bond cleavage. The reaction follows the same steps as the transamination reaction but does not hydrolyze the tautomerized Schiff base. The proposed reaction mechanism involves an attack of an enzyme nucleophile on the carbonyl carbon (Cγ) of the tautomerized 3hKyn-PLP Schiff base. This is followed by Cβ-Cγ bond cleavage to generate an acyl-enzyme intermediate together with a tautomerized Ala-PLP adduct. Hydrolysis of the acyl-enzyme then yields 3hAnt.