Renal glutamine utilization: glycylglycine stimulation of gamma-glutamyltransferase.
Glycylglycine stimulation of renal glutamine utilization was studied on the homogenate, subcellular and purified enzyme level. The results clearly establish the existence of two glutamine utilizing pathways, the mitochondrial dependent L-glutamine amidohydrolase (PDG) and a second, extramitochondrial pathway. In contrast to the mitochondrial pathway which produces stoichiometric amounts of ammonia and glutamate, this second pathway hydrolyzes glutamine to produce ammonia and transfers the gamma-glutamyl moiety, producing gamma-glutamyl peptides. In the crude systems, containing cyclotransferase, the gamma-glutamyl moiety appears mainly as 5-oxoproline; however, in the enzyme preparation, purified 112-fold, gamma-glutamyl peptides (transpeptidation) and a small amount of glutamate (hydrolysis) appear. D-Glutamine was also hydrolyzed, in contrast to the stereospecific PDG, but at less than one-half the rate of the L-isomer. The molecular weight of this extramitochondrial D- and L-glutamine utilizing enzyme was estimated by gel filtration on a Sephadex G-200 column and found to be approximately 70 000. Based on product formation, molecular weight estimation and copurification with the activity responsible for p-nitroanilide release from gamma-glutamyl-p-nitroanilide, we conclude that this reaction is catalyzed by gamma-glutamyltranspeptidase. Glycylglycine stimulated this enzyme to produce more ammonia while decreasing the appearance of glutamate; in contrast, the mitochondrial glutaminase was unaffected by glycylglycine. This extramitochondrial glutamine utilizing pathway can make a significant contribution to in vivo renal ammoniagenesis.
D000818:Animals; D004151:Dipeptides / Q000494:pharmacology*; D004789:Enzyme Activation; D005973:Glutamine / Q000378:metabolism*; D006033:Glycylglycine / Q000494:pharmacology*; D007668:Kidney / Q000201:enzymology*; D007700:Kinetics; D008297:Male; D051381:Rats; D005723:gamma-Glutamyltransferase / Q000378:metabolism*
D004151:Dipeptides; D005973:Glutamine; D006033:Glycylglycine; D005723:gamma-Glutamyltransferase