Intermediates of the gamma-glutamyl cycle in mouse tissues. Influence of administration of amino acids on pyrrolidone carboxylate and gamma-glutamyl amino acids.
GAMMA-Glutamyl transpeptidase, gamma-glutamyl cyclotransferase, L-pyrrolidone carboxylate hydrolase, gamma-glutamylcysteine synthetase and glutathione synthetase, the enzymes of the gamma-glutamyl cycle, were found in mouse brain, liver and kidney. The activity of L-pyrrolidone carboxylate hydrolase was many times lower than the activities of the other enzymes, and thus the conversion of L-pyrrolidone carboxylate to L-glutamate is likely to be the rate-limiting step of the cycle. The specificity of gamma-glutamyl cyclotransferase from mouse tissues was similar to that from rat tissues. The concentration of pyrrolidone carboxylate and gamma-glutamyl amino acids, intermediates of the gamma-glutamyl cycle, was determined by a gas chromatographic procedure coupled with electron capture detection. Administration of L-2-aminobutyrate, an amino acid that is utilized as substrate in the reaction catalyzed by gamma-glutamylcysteine synthetase, led to a large accumulation of gamma-glutamyl-2-aminobutyrate and pyrrolidone carboxylate in mouse tissues. L-Methionine-RS-sulfoximine, an inhibitor of gamma-glutamylcysteine synthetase, abolished the increase in concentration of pyrrolidone carboxylate. No accumulation of pyrrolidone carboxylate was observed after L-cysteine. The separate administration of several protein amino acids had little effect on the concentration of pyrrolidone carboxylate; however formation of small amounts of the corresponding gamma-glutamyl derivatives (e.g. gamma-glutamylmethionine and gamma-glutamylphenylalanine) was detected. These intermediates are probably formed by transpeptidation between glutathione and the corresponding amino acid, catalyzed by gamma-glutamyl transpeptidase. The concentration of pyrrolidone carboxylate increased significantly after administration of a mixture containing all protein amino acids, the highest increase occurring in the kidney. The results suggest that two separate pathways for the formation of gamma-glutamyl amino acids and pyrrolidone carboxylate exist in vivo. One of these results from the function of gamma-glutamylcysteine synthetase in glutathione synthesis. The other pathway involves the amino-acid-dependent degradation of glutathione, mediatedby gamma-glutamyl transpeptidase. Only very small amounts of free intermediates are apparently derived from the latter pathway, suggesting that the gamma-glutamyl amino acids formed in this pathway are either enzyme-bound or are directly hydrolyzed to glutamate and free amino acid.
D000596:Amino Acids / Q000494:pharmacology*; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D002849:Chromatography, Gas; D005971:Glutamates / Q000378:metabolism*; D005978:Glutathione; D005998:Glycine / Q000378:metabolism; D007668:Kidney / Q000187:drug effects / Q000378:metabolism*; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D051379:Mice; D009928:Organ Specificity; D010453:Peptide Synthases / Q000378:metabolism; D011752:Pyroglutamate Hydrolase / Q000378:metabolism; D011760:Pyrrolidinones / Q000378:metabolism*; D011761:Pyrrolidonecarboxylic Acid / Q000378:metabolism*; D005722:gamma-Glutamylcyclotransferase / Q000378:metabolism; D005723:gamma-Glutamyltransferase / Q000378:metabolism
D000596:Amino Acids; D005971:Glutamates; D011760:Pyrrolidinones; D005723:gamma-Glutamyltransferase; D011752:Pyroglutamate Hydrolase; D005722:gamma-Glutamylcyclotransferase; D010453:Peptide Synthases; D005978:Glutathione; D011761:Pyrrolidonecarboxylic Acid; D005998:Glycine