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1Schools of Biochemistry and Molecular Genetics, The University of New South Wales, Sydney, NSW 2052, Australia
2Microbiology and Immunology, The University of New South Wales, Sydney, NSW 2052, Australia
3Author for correspondence: George L. Mendz. Tel: +61 2 385 2042. Fax: +61 2 313 62712. e-mail: G.Mendz@unsw.EDU.AU
ABSTRACT
The presence and activities of the enzymes of the urea cycle in the bacterium Helicobacter pylori were investigated employing one- and two-dimensional NMR spectroscopy and radioactive tracer analysis. Cell suspensions, lysates and membrane preparations generated L-ornithine and ammonium at high rates in incubations with L-arginine, indicating the presence of arginase activity. Anabolic ornithine transcarbamoylase (OTCase) 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 incubations of cell-free extracts with citrulline radiolabelled in the guanidino moiety revealed the presence of catabolic OTCase activity. Argininosuccinate formation and catalysis indicated the presence of argininosuccinate synthetase and argininosuccinase activities. The findings suggested that H. pylori has a urea cycle which acts as an effective mechanism to extrude excess nitrogen from cells.
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