Stereochemistry of conversion of the suicide substrates β-chloro-D-alanine-and D- and L-serine O-sulfates into pyruvate by D-amino acid aminotransferase and by L-aspartate aminotransferase

Abstract

β-Chloro-D-alanine and D-serine O-sulfate are converted into a putative aminoacrylate intermediate by D-amino acid aminotransferase. This either reacts with pyridoxal phosphate to form a reactive inhibitor of the enzyme or it is protonated and hydrolysed to give pyruvate. The protonation reaction is shown to occur with modest stereoselectivity, indicating overall retention of stereochemistry in replacement of the leaving group by hydrogen. The corresponding reaction of L-serine O-sulfate using L-aspartate aminotransferase shows little or no stereosetectivity.