DE-NOVO SYNTHESIS OF PYRIMIDINE NUCLEOTIDES BY HELICOBACTER-PYLORI

The incorporation of pyrimidine nucleotide precursors into Helicobacte r pylori and the activities of enzymes involved in their synthetic pat hways were investigated by radioactive tracer analysis and P-31 nuclea r magnetic resonance spectroscopy. The bacterium was found to take up aspartate and bicarbonate and to incorporate carbon atoms from these p recursors into its genomic DNA. Orotate, an intermediate of de novo py rimidine biosynthesis, and uracil and uridine, precursors for pyrimidi ne pathways, were also incorporated by the micro-organism. Radiolabell ed substrates were used to assess the activities of aspartate transcar bamoylase, orotate phosphoribosyltransferase, orotidylate decarboxylas e, CTP synthetase, uracil phosphoribosyltransferase, thymidine kinase and deoxycytidine kinase in bacterial lysates. The study provided evid ence for the presence in H. pylori of an operational de nova pathway, and a less active salvage pathway for the biosynthesis of pyrimidine n ucleotides.