Conversion of glutathione to glutathione disulfide by cell membrane-bound oxidase activity
An apparently specific glutathione oxidase activity is present in renal cortex, epididymal caput, jejunal villus tip cells, choroid plexus, and retina (but not in liver). The activity is membrane-bound and is localized on the luminal surface of the brush border membranes of the kidney and jejunum. The distribution and localization of the oxidase are similar to those of gamma-glutamyl transpeptidase, suggesting that there is a significant relationship among the translocation of intracellular glutathione, the extracellular oxidation of glutathione to glutathione disulfide, and the reactions of the gamma-glutamyl cycle. Thus, both glutathione present in the blood plasma and intracellular glutathione translocated to the cell surface are accessible to oxidation and transpeptidation. Acceptor substrates of the transpeptidase (e.g., L amino acids) promote transpeptidation and decrease oxidation of glutathione. Conversion of glutathione to glutathione disulfide is followed by utilization of the latter compound by gamma-glutamyl transpeptidase and dipeptidase. Although intracellular oxidation of glutathione to glutathione disulfide is readily reversed by the action of glutathione reductase, glutathione disulfide formed extracellularly cannot be reduced; instead, it undergoes hydrolytic and transpeptidation reactions leading to gamma-glutamyl amino acid and amino acid products which may be recovered by being transported into the cell.