gamma-Glutamyl amino acids. Transport and conversion to 5-oxoproline in the kidney.
Transport of gamma-glutamyl amino acids, a step in the proposed glutathione-gamma-glutamyl transpeptidase-mediated amino acid transport pathway, was examined in mouse kidney. The transport of gamma-glutamyl amino acids was demonstrated in vitro in studies on kidney slices. Transport was followed by measuring uptake of 35S after incubation of the slices in media containing gamma-glutamyl methionine [35S]sulfone. The experimental complication associated with extracellular conversion of the gamma-glutamyl amino acid to amino acid and uptake of the latter by slices was overcome by using 5-oxoproline formation (catalyzed by intracellular gamma-glutamyl-cyclotransferase) as an indicator of gamma-glutamyl amino acid transport. This method was also successfully applied to studies on transport of gamma-glutamyl amino acids in vivo. Transport of gamma-glutamyl amino acids in vitro and in vivo is inhibited by several inhibitors of gamma-glutamyl transpeptidase and also by high extracellular levels of glutathione. This seems to explain urinary excretion of gamma-glutamylcystine by humans with gamma-glutamyl transpeptidase deficiency and by mice treated with inhibitors of this enzyme. Mice depleted of glutathione by treatment with buthionine sulfoximine (which inhibits glutathione synthesis) or by treatment with 2,6-dimethyl-2,5-heptadiene-4-one (which effectively interacts with tissue glutathione) exhibited significantly less transport of gamma-glutamyl amino acids than did untreated controls. The findings suggest that intracellular glutathione functions in transport of gamma-glutamyl amino acids. Evidence was also obtained for transport of gamma-glutamyl gamma-glutamylphenylalanine into kidney slices.
D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport; D005971:Glutamates / Q000378:metabolism; D005978:Glutathione / Q000037:antagonists & inhibitors / Q000378:metabolism; D066298:In Vitro Techniques; D007668:Kidney / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D011760:Pyrrolidinones / Q000096:biosynthesis*; D011761:Pyrrolidonecarboxylic Acid / Q000096:biosynthesis*; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D013462:Sulfur Radioisotopes
D000596:Amino Acids; D005971:Glutamates; D011760:Pyrrolidinones; D013462:Sulfur Radioisotopes; D005978:Glutathione; D011761:Pyrrolidonecarboxylic Acid