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.