Nitrogen Metabolism

The study of nitrogen metabolism in Helicobacter pylori was initially made possible by the development of defined growth media, which permitted (i) the determination of the minimal amino acid requirements of this bacterium and (ii) the following of the fate of amino acids in whole bacteria. The subsequent publication of the complete genomic sequences of two H. pylori strains, 26695 and J99, has confirmed some of the data obtained and supplied additional genetic information. H. pylori is auxotrophic for several amino acids, supporting the idea that its growth in vivo is strictly dependent on the gastric environment. Large amounts of amino acids, dipeptides, and polypeptides are present in the gastric juice owing to the activities of enzymes such as pepsin, which break down proteins efficiently. Amino acid utilization by H. pylori grown in a defined medium has been investigated by nuclear magnetic resonance (NMR) spectroscopy and amino acid analysis. Nitrogen metabolism in H. pylori generates considerable amounts of free ammonia that either could be incorporated into proteins via the glutamine synthetase (GS-ase) pathway or released into the external environment by diffusion in its NH3 form. The possibility that H. pylori has a urea cycle was investigated by assessing the activity of the four enzymes of this cycle: arginase, anabolic ornithine transcarbamoylase (OTC-ase), arginosuccinate synthetase, and arginosuccinase, employing one- and two-dimensional NMR spectroscopy and radioactive tracer analysis.