The control of de novo pyrimidine biosynthesis in the industrially important patent strain "Pseudomonas alkanolytica" ATCC 21034 was investigated. Uracil supplementation of succinate-grown "P. alkanolytica" cells produced the greatest depression of the de novo pyrimidine biosynthetic pathway enzyme activities. After the pyrimidine limitation of a "P. alkanolytica" orotate phosphoribosyltransferase mutant strain grown on succinate, the pyrimidine biosynthetic pathway enzyme activities were derepressed. The pyrimidine biosynthetic pathway enzyme aspartate transcarbamoylase in "P. alkanolytica" was inhibited by pyrophosphate, cytidine 5'-triphosphate (CTP), uridine 5'-triphosphate (UTP), and guanosine 5'-triphosphate (GTP).