Biosynthesis of pyrimidine nucleotides
The de novo synthesis of pyrimidine nucleotides is different from purine nucleotides. The elements of the pyrimidine ring are derived from glutamine, carbon dioxide and aspartate. Acid is characterized by first synthesizing these raw materials into a pyrimidine ring and then reacting with PRPP to generate it.
①
Synthesis of pyrimidine ring: glutamine and carbon dioxide are powered by ATP in the cytosol, and are catalyzed by carbamoyl synthase II to generate carbamoyl phosphate. The latter, catalyzed by aspartate transcarbamylase, transfers the carbamoyl group to the amino group of aspartate to generate carbamoyl aspartate. Carbamyl aspartic acid is dehydrated and cyclized to generate dihydroorotic acid, which is then dehydrogenated to form orotic acid (pyrimidine derivative).
②
Synthesis of uracil nucleotides (UMP) and cytosine nucleotides (cMP): Orotic acid reacts with PRPP to generate orotic acid nucleotides, which Decarboxylation becomes uridylic acid.
Uridylic acid is the precursor of all other pyrimidine nucleotides. The conversion of uracil nucleotides to cytosine nucleotides occurs at the nucleoside triphosphate level. UMP is catalyzed by the corresponding kinase to generate UDP and UTP, and glutamine provides the amino group to convert UTP into CTP.