Action of Liver Glutamine Transaminase and l-Amino Acid Oxidase on Several Glutamine Analogs

The l-glutamine analogs, l-albizziin (l-α-amino-β-ureido-propionic acid), S-carbamyl-l-cysteine, and O-carbamyl-l-serine were found to be substrates for purified rat liver glutamine transaminase, and the α-keto acid product formed in each case was found to cyclize to a lactam analogous in structure to the cyclic form of α-ketoglutaramic acid (2-pyrrolidone-5-hydroxy-5-carboxylic acid). Evidence was obtained that the initial product of transamination of albizziin, S-carbamylcysteine, and O-carbamylserine are the corresponding α-keto acids, which were found to be converted by ω-amidase (followed by spontaneous decarboxylation) to β-aminopyruvate, β-mercaptopyruvate, and β-hydroxypyruvate, respectively. Incubation of the glutamine analogs with l-amino acid oxidase from Crotalus adamanteus venom gave the corresponding cyclic lactam forms; the products obtained from albizziin and S-carbamyl-cysteine were rapidly and irreversibly dehydrated in acid or base to yield 2-imidazolinone-4-carboxylic acid and 2-thiazolinone-4-carboxylic acid, respectively. Neither α-ketoglutaramate nor 2-oxazolidone-4-hydroxy-4-carboxylic acid (which was isolated as the corresponding barium salt) was dehydrated under these conditions.