The first two enzymes of pyrimidine nucleotides biosynthesis is sensitive to allosteric regulation with respect to the regulation of gene expression. The first three and the last two enzymes of the pathway are regulated by apparently coordinate repression and depression. Carbamoyl phosphate synthase is inhibited by UTP and purine nucleotides but is activated by PRPP. Aspartate transcarbamoylase is particularly sensitive to inhibition by CTP as shown in Figure 11.8.

Figure 11.8 Regulation of Pyrimidine Synthesis