CHEMICAL MODIFICATION OF BACTERIAL 4-AMINOBUTYRATE AMINOTRANSFERASE BY PHENYLGLYOXAL

4-Aminobutyrate aminotransferase (EC 2.6.1.19), obtained from Pseudomo nas fluorescens, was irreversibly inhibited by phenylglyoxal, a reagen t that specifically modifies arginyl residues. The inactivation appear ed to be the result of a simple, bimolecular reaction since no evidenc e of a reversible complex between inhibitor and enzyme emerged. The se cond-order rate constant was 0.221+/-0.077 M(-1) sec(-1). The concentr ation of either substrate had no effect on the inhibition, but an incr ease in the concentration of pyridoxal 5'-phosphate reduced the rate o f inactivation by phenylglyoxal. The data are consistent with the modi fication of amino acid residues at the cofactor binding site on the en zyme.