Regulation of the Pyrimidine Biosynthetic Pathway in <Emphasis Type="Italic">Pseudomonas mucidolens</Emphasis>

Control of pyrimidine biosynthesis was examined in Pseudomonas mucidolens ATCC 4685 and the five de novo pyrimidine biosynthetic enzyme activities unique to this pathway were influenced by pyrimidine supplementation in cells grown on glucose or succinate as a carbon source. When uracil was supplemented to glucose-grown ATCC 4685 cells, activities of four de novo enzymes were 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 glucose-grown mutant strain cells, pyrimidine limitation of this strain caused aspartate transcarbamoylase, dihydroorotase and dihydroorotate dehydrogenase activities to increase by more than 3-fold while OMP decarboxylase activity increased by 2.7-fold. The syntheses of the de novo enzymes appeared to be regulated by pyrimidines. At the level of enzyme activity, aspartate transcarbamoylase activity in P. mucidolens ATCC 4685 was subject to inhibition at saturating substrate concentrations. Transcarbamoylase activity was strongly inhibited by UTP, ADP, ATP, GTP and pyrophosphate.