The inhibition of glutamate dehydrogenase by L-serine O-sulphate and related compounds and by photo-oxidation in the presence of Rose Bengal.

1. Glutamate dehydrogenase was inhibited by l-serine O-sulphate, beta-chloro-l-alanine, O-phospho-l-serine and beta-chloro-l-alanine methyl ester. With the exception of beta-chloro-l-alanine methyl ester which was an irreversible inhibitor, it was possible to reverse the inhibitory effects by dialysis. 2. Both NAD(+) and glutamate afford some protection against the inhibition due to the methyl ester. No change in the normal stimulatory effect exhibited by ADP was observed in the presence of beta-chloro-l-alanine methyl ester but the effect due to GTP was modified. 3. Irradiation of glutamate dehydrogenase in the presence of Rose Bengal produced rapid inactivation. Amino acid analysis of the inactivated enzyme showed that eight histidine residues had been destroyed in the process.