The regulation of de novo pyrimidine biosynthesis in Pseudomonas putida ATCC 17536 by pyrimidines was explored. The pathway enzyme activities were higher in glucose-grown cells than in succinate-grown cells, indicating catabolite repression by succinate. In P. putida cells grown on succinate as a carbon source, only aspartate transcarbamoylase activity was greatly diminished by uracil supplementation. When glucose was the carbon source, orotic acid supplementation significantly decreased orotate phosphoribosyltransferase and orotidine 5'-monophosphate (OMP) decarboxylase activities. Uracil auxotrophs, deficient for dihydroorotase activity or with reduced phosphoribosyltransferase activity, were isolated. After pyrimidine limitation of both auxotrophs, the greatest derepression of enzyme activity was observed for OMP decarboxylase independent of carbon source. Orotic acid induced both phosphoribosyltransferase and decarboxylase activities in glucose-grown cells of the dihydroorotase-deficient strain. Regulation at the transcriptional level of de novo pyrimidine biosynthetic enzyme synthesis in P. putida ATCC 17536 was observed, which contrasts with previous observations.
The effect of carbon source on the regulation of the de novo pyrimidine biosynthetic enzymes in Pseudomonas alcaligenes ATCC 14909 was investigated. The de novo pyrimidine biosynthetic enzymes were measured in extracts of P. alcaligenes ATCC 14909 cells and of cells from an auxotroph deficient for orotate phosphoribosyltransferase activity. Pyrimidine biosynthetic enzyme activities in ATCC 14909 were influenced by pyrimidine supplementation to the culture medium but not by the carbon source present. Pyrimidine limitation of the auxotroph elevated the de novo enzyme activities indicating that this pathway may be controlled at the transcriptional level by a pyrimidine-related compound. Its regulation seemed to be subject to less transcriptional control by a pyrimidine-related compound than what was observed in the closely related species Pseudomonas pseudoalcaligenes.
The effect of carbon source on the regulation of the de novo pyrimidine biosynthetic enzymes in the bacterium Pseudomonas mendocina was studied. When glucose was the carbon source, orotic acid supplementation of P. mendocina cells produced the greatest depression of aspartate transcarbamoylase, dihydroorotate dehydrogenase and orotate phosphoribosyltransferase activities while P. mendocina cells grown in the presence of uracil caused the maximal decrease in dihydroorotase and OMP decarboxylase activities. After the pyrimidine starvation of an orotate phosphoribosyltransferase mutant strain of P. mendocina grown on glucose, the pyrimidine biosynthetic pathway enzyme activities were generally diminished. With respect to pyrimidine starvation studies, the carbon source glucose appeared to lessen regulation at the level of enzyme synthesis compared to what has been observed when succinate served as the carbon source. The regulation of the pyrimidine biosynthetic pathway by carbon source in P. mendocina appeared to differ from how carbon source influenced the control of pyrimidine biosynthesis in the closely-related species Pseudomonas stutzeri.
Regulation of the de novo pyrimidine biosynthetic enzymes in the bacterium Pseudomonas mendocina was examined when its cells were grown on succinate as a carbon source. When P. mendocina was grown in the presence of orotic acid or uracil, the de novo enzyme activities were depressed with dihydroorotase activity being significantly depressed after uracil addition. Following pyrimidine limitation of a uracil auxotroph of P. mendocina deficient for orotate phosphoribosyltransferase activity, the pyrimidine biosynthetic pathway enzyme activities were affected indicating possible regulation at the level of enzyme synthesis. Of the de novo pathway enzymes assayed, dihydroorotate dehydrogenase exhibited the highest increase in its activity. The regulation of the pyrimidine biosynthetic pathway by pyrimidines in P. mendocina appeared similar to what was previously observed for the taxonomically‐related species P. stutzeri.
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