Proposed role of glutathione in L-methionine transport across rabbit renal brush border membranes.

Glutathione has been proposed as responsible for amino acid transport across the brush border membrane of the kidney. According to the gamma glutamyl cycle hypothesis, gamma glutamyl transpeptidase, an enzyme bound to brush border membranes, interacts with intracellular glutathione and an extracellular amino acid, incurring formation of gamma glutamyl-amino acid which is then transported into the cell. The hypothesis further holds that glutathione levels are held constant by a reaction cycle involving 5 cytosolic enzymes and the utilization of 3 moles of ATP. We evaluated this hypothesis, using a brush border vesicle system from rabbit renal proximal tubule. The vesicles enabled study of the transport of L-methionine in a system free of other factors that might influence glutathione. The results suggest that glutathione alone does not enhance the influx of methionine.