Glutathione: interorgan translocation, turnover, and metabolism

Glutathione is translocated out of cells; cells that have membrane-bound gamma-glutamyl transpeptidase can utilize translocated glutathione, whereas glutathione exported from cells that do not have appreciable transpeptidase enters the blood plasma. Glutathione is removed from the plasma by the kidney and other organs that have transpeptidase. Studies in which mice and rats were treated with buthionine sulfoximine, a selective and potent inhibitor of gamma-glutamylcysteine synthetase and therefore of glutathione synthesis, show that glutathione turns over at a significant rate in many tissues, especially kidney, liver, and pancreas; the rate of turnover in mouse skeletal muscle is about 60% of that in the kidney. Experiments on rats surgically deprived of one or both kidneys and treated with the gamma-glutamyl transpeptidase inhibitor D-gamma-glutamyl-(o-carboxy)phenylhydrazide establish that extrarenal gamma-glutamyl transpeptidase activity accounts for the utilization of about one-third of the total blood plasma glutathione. Normal animals treated with the transpeptidase inhibitor excrete large amounts of glutathione in their urine. They also excrete gamma-glutamylcysteine, suggesting that cleavage of glutathione at the cysteinylglycine bond may be of metabolic significance. The present and earlier findings lead to a tentative scheme (presented here) for the metabolism and translocation of glutathione, gamma-glutamyl amino acids, and related compounds.