Stereochemistry of the reaction of the inhibitor β-chloroalanine with mercaptoethanol, a β-substitution reaction catalysed by an aminotransferase

L-Aspartate aminotransferase, a member of the alpha-family of PLP mediated enzymes, which normally catalyses transamination, has been used to catalyse the beta-substitution reaction of stereospecifically labelled samples of the enzyme inhibitor beta-chloro-L-alanine with 2-mercaptoethanol; the stereochemistry of the products was assigned by independent synthesis, showing that the abnormal substitution reaction proceeds with overall retention of stereochemistry, the usual stereochemical consequence of reactions catalysed by enzymes of the beta-family of PLP mediated enzymes which have low homology with enzymes of the alpha-family.