title: Formation of 5-oxoproline from glutathione in erythrocytes by the gamma-glutamyltranspeptidase-cyclotransferase pathway.
abstract: gamma-Glutamyltranspeptidase activity was demonstrated in the membrane fraction of rabbit erythrocytes. The activity observed (with glutathione and various amino-acid acceptors) was similar in magnitude to that of the gamma-glutamylcyclotransferase and gamma-glutamylcysteine synthetase activities found in the soluble fraction of the cell. No transpeptidase activity was observed with either gamma-glutamyl p-nitroanilide or oxidized glutathione in contrast to the rabbit-kidney enzyme for which these compounds and glutathione serve as substrates. Erythrocyte suspensions and hemolysates formed 5-oxoproline (pyroglutamate; pyrrolidone carboxylate); the rate of 5-oxoproline formation from glutathione by hemolysates was increased by addition of methionine. The findings indicate that 5-oxoproline is an end-product of glutathione metabolism in erythrocytes, and that 5-oxoproline passes out of the erythrocyte and is metabolized in other tissues. The observed rate of 5-oxoproline formation is consistent with the conclusion that the gamma-glutamyltranspeptidase-cyclotransferase pathway, together with the synthesis of glutathione from glycine, cysteine, and glutamate, account for a large fraction of the observed amino-acid turnover of erythrocyte glutathione.
mesh_terms: D000217:Acyltransferases / Q000097:blood*; D000818:Animals; D002250:Carbon Radioisotopes; D002462:Cell Membrane / Q000201:enzymology; D003545:Cysteine / Q000378:metabolism; D004150:Dipeptidases / Q000097:blood; D004912:Erythrocytes / Q000166:cytology / Q000201:enzymology*; D005971:Glutamates / Q000378:metabolism; D005978:Glutathione / Q000096:biosynthesis / Q000378:metabolism; D005998:Glycine / Q000378:metabolism; D066298:In Vitro Techniques; D008715:Methionine / Q000378:metabolism; D010453:Peptide Synthases / Q000097:blood; D011761:Pyrrolidonecarboxylic Acid / Q000096:biosynthesis; D011817:Rabbits; D005723:gamma-Glutamyltransferase / Q000097:blood*
chemical_list: D002250:Carbon Radioisotopes; D005971:Glutamates; D008715:Methionine; D000217:Acyltransferases; D005723:gamma-Glutamyltransferase; D004150:Dipeptidases; D010453:Peptide Synthases; D005978:Glutathione; D003545:Cysteine; D011761:Pyrrolidonecarboxylic Acid; D005998:Glycine