A reaction pathway for transimination of the pyridoxal 5'-phosphate in D-serine dehydratase by amino acids.

Transimination of the enzyme-linked cofactor by an amino acid is the first chemical transformation in the reactions catalyzed by pyridoxal 5'-phosphate-requiring enzymes. In this work, stopped flow fluorimetry was used to characterize the kinetics of transimination of the cofactor in D-serine dehydratase by several amino acids. The results of these studies indicate that transimination is a multistep process, the first step of which is probably formation of a noncovalent complex between the enzyme and the amino acid. D-Serine dehydratase was found to exhibit considerable specificity in the transimination reaction. Furthermore, the enzyme was shown to facilitate the transimination reaction with amino acids and inhibit transimination of the bound cofactor by amines lacking a carboxylate group. A reaction pathway was proposed for the transimination process which accounts for the specificity of the enzyme and indicates the changes in the conformation of the bound cofactor as dictated by the stereoelectronic requirements of the transimination reaction.