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Proceedings of the National Academy of Sciences of the United States of America logoLink to Proceedings of the National Academy of Sciences of the United States of America
. 1974 Feb;71(2):293–297. doi: 10.1073/pnas.71.2.293

Formation of 5-Oxoproline from Glutathione in Erythrocytes by the γ-Glutamyltranspeptidase-Cyclotransferase Pathway

Anil G Palekar 1, Suresh S Tate 1, Alton Meister 1
PMCID: PMC387989  PMID: 4150022

Abstract

γ-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 γ-glutamylcyclotransferase and γ-glutamylcysteine synthetase activities found in the soluble fraction of the cell. No transpeptidase activity was observed with either γ-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 γ-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.

Keywords: pyroglutamate, pyrrolidone carboxylate, γ-glutamyl cycle, γ-glutamyl cyclotransferase

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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