| Summary: | Thesis (Ph.D.)--Memorial University of Newfoundland, 1976. Biochemistry Bibliography : leaves 150-157 Urinary excretion of ammonia facilitates excretion of strong acids and serves to conserve body stores of- sodium. This ammonia is provided mainly by the renal hydrolysis of gltamine catalyzed by the gluta- minase isoenzyrnes. The subcellular Iocalization of the isoenzymes of glutaminase has been studied in rat kidney, cortex and liver. Differential centrifugation and sucrose density gradient techniques demon-strated a mitochondrial localization for phosphate dependent glutaminase in both liver and kidney cortex. Fractionation of isolated mitochondria by digitonin and by sonication revealed that phosphate-dependent gliltaminase is located in the mitochondrial matrix compartment , a finding in agreement with its demonstrable latency. -- The highest specific activity of phosphate-independent glutaminase was found in the microsomal fraction of rat kidney cortex on differential centrifugation. This fraction was also enriched in NADPH-cytochrome c reductase (endoplasmic reticulum marker) ,5'-nucleotidase (plasma membrane marker), alkaline phosphatase, y-glutamyltranspeptidase and maltase (brush border markers). Continuous sucrose density gradient studies on acrosomal fractions showed that phosphate-indeminase was located, in the brush border membranes, of rat kidney cortex. This enzyme is truly membranous as it couldnot be removed by sonication, salt treatment or pH alterations. -- Further studies on phosphate-independent glutaminase and y-glutamyl transferring activities of rat kidney cortex showed that phosphate-1 independent glutaminase enzyme appears to be a single hydrolase which catalyses the hydrolosis of glutamine, glutathione, y-gluamylhydroxamate and y-gluamyl-p-nitroanilide. The enzyme activity was stimulated in the presence of maleate and competition between the substrates was observed. Phosphate-independent glutaminase activity was not attributed to the glutamine synthetase and it also appeared to be different from y-glutamyltransferase activity. Phosphate-independent glutaminase and y-glutamyltranspeptidase activities were lost to identical extents by various heat treatments , were removed identically from brush border membranes by papain treatment and were co-purified, on Sephadex G-100 r. Glutamine was shown to inhibit y-glutamyltranspeptidase competitively with y-gluamyl-p-nitroanilide. These studies suggests that phosphate-independent glutaminase and y-glutamyltranspeptidase represent different catalytic actions of the same enzyme.
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