Regulation of pyrimidine nucleotide biosynthesis in Pseudomonas synxantha

Regulation of pyrimidine nucleotide biosynthesis in Pseudomonas synxantha ATCC 9890 was investigated and the pyrimidine biosynthetic pathway enzyme activities were affected by pyrimidine supplementation in cells grown on glucose or succinate as a carbon source. In pyrimidine-grown ATCC 9890 cells, the activities of four de novo enzymes could be depressed which indicated possible repression of enzyme synthesis. To learn whether the pathway was repressible, pyrimidine limitation experiments were conducted using an orotate phosphoribosyltransferase (pyrE) mutant strain identified in this study. Compared to excess uracil growth conditions for the succinate-grown mutant strain cells, pyrimidine limitation of this strain caused dihydroorotase activity to increase about 3-fold while dihydroorotate dehydrogenase and orotidine 5'-monophosphate decarboxylase activities rose about 2-fold. Regulation of de novo pathway enzyme synthesis by pyrimidines appeared to be occurring. At the level of enzyme activity, aspartate transcarbamoylase activity in P. synxantha ATCC 9890 was strongly inhibited in vitro by pyrophosphate, UTP, ADP, ATP, CTP and GTP under saturating substrate concentrations.