The site at which 4-iodoacetamidosalicylate reacts with glutamate dehydrogenases

Abstract

1. Bovine, porcine and chicken liver glutamate dehydrogenases were irreversibly inhibited by a tenfold excess of radioactive 4-iodoacetamidosalicylic acid at pH7.5. 2. Inhibition was accompanied by the covalent incorporation of 1.1 mol of labelled inhibitor/mol of polypeptide chain. Acid hydrolysis yielded Nε-carboxymethyl-lysine as the sole labelled amino acid. No labelled S-carboxymethylcysteine was recovered from the bovine or porcine enzymes. 3. The labelled bovine enzyme was hydrolysed with trypsin. The radioactivity was found at lysine-126 in a peptide comprising residues 119–130 of the sequence. 4. The amino acid compositions of the tryptic peptides containing labelled lysine from the porcine and chicken enzymes were similar to that of the bovine peptide.