THE UREA CYCLE OF HELICOBACTER-PYLORI

The presence and activities of the enzymes of the urea cycle in the ba cterium Helicobacter pylori were investigated employing one- and two-d imensional NMR spectroscopy and radioactive tracer analysis. Cell susp ensions, lysates and membrane preparations generated L-ornithine and a mmonium at high rates in incubations with L-arginine. indicating the p resence of arginase activity. Anabolic ornithine transcarbamoylase (OT Case) activity was identified by the formation of heat-stable products in incubations of cell-free extracts with ornithine and radiolabelled carbamoyl phosphate. The heat-labile product that resulted from incub ations of cell-free extracts with citrulline radiolabelled in the guan idino moiety revealed the presence of catabolic OTCase activity. Argin inosuccinate formation and catalysis indicated the presence of arginin osuccinate synthetase and argininosuccinase activities. The findings s uggested that H. pylori has a urea cycle which acts as an effective me chanism to extrude excess nitrogen from cells.