Metabolism of gamma-glutamyl amino acids and peptides in mouse liver and kidney in vivo.

The metabolism in vivo of gamma-glutamyl amino acids and peptides was studied in the mouse after administration of loading doses of L-gamma-glutamyl-2-aminobutyrate and several other gamma-glutamyl compounds, including glutathione. A great and rapid accumulation of glutamate, glutamine, aspartate and pyrrolidone carboxylate was observed in the kidney. Similarly, after administration of a tracer dose of L-gamma-[14C]glutamyl-L-2-aminobutyrate a rapid incorporation of label into kidney glutamate, glutamine and aspartate was found. These results suggest that both the hydrolytic and gamma-glutamyl transfer reactions catalyzed by gamma-glutamyl transpeptidase are active in the renal handling of gamma-glutamyl compounds. Indirect evidence was obtained that L-gamma-glutamyl-2-aminobutyrate is partially taken up by the kidney cell in an intact form. In contrast to the kidney, administration of several gamma-glutamyl derivatives did not cause an increase in liver glutamate, glutamine and pyrrolidone carboxylate. After administration of L-gamma-glutamyl-2-aminobutyrate only a slight increase in liver aspartate and pyrrolidone carboxylate was observed. Experiments with L-gamma-[14C]glutamyl-L-2-aminobutyrate suggest that this derivative is largely first degraded to its component amino acids (probably in the kidney) before entering into the metabolism of the liver cell. gamma-Glutamyl transpeptidase may function in the metabolism and transport of glutathione and other gamma-glutamyl compounds in a manner analogous to the function of dipeptidases and disaccharidases in the metabolism and transport of dipeptides and disaccharides respectively.