描述
Pyrimidine is a heterocyclic aromatic organic compound similar to benzene and pyridine, containing two nitrogen atoms at positions 1 and 3 of the six-member ring. Pyrimidines are heterocyclic, six-membered, nitrogen-containing carbon ring structures, with uracil, cytosine and thymine being the basal structures of ribose-containing nucleosides (uridine, cytidine and thymidine respectively), or deoxyribose-containing deoxynucleosides, and their corresponding ribonucleotides or deoxyribonucleotides. Pyrimidines serve essential functions in human metabolism as ribonucleotide bases in RNA (uracil and cytosine), and as deoxyribonucleotide bases in DNA (cytosine and thymine), and are linked by phosphodiester bridges to purine nucleotides in double-stranded DNA, in both the nucleus and the mitochondria. Pyrimidine activated sugars are also involved in polysaccharide and phospholipid synthesis, glucuronidation in detoxification processes, glycosylation of proteins and lipids and in the recently identified novel endothelium-derived vasoactive dinucleotides.
Pyrimidines are synthesized de novo from simple precursors. Synthesis occurs in six steps, with cellular compartmentalization of specific steps in the cytosol or mitochondria, enabling changes in metabolic rate with need. Pyrimidine synthesis differs from purine synthesis, in that the single pyrimidine ring is assembled first and is then linked to ribose phosphate to form UMP. The enzymes that catalyse UMP synthesis, CAD [carbamoylphosphate synthetase II (CPSII), aspartate transcarbamoylase (ATCasea) and dihydroorotase (DHOase)], dihydroorotate dehydrogenase (DHODH) and uridine monophosphate synthase (UMPS), are encoded by only three genes - CAD, DHODH and UMPS (chromosomal locations 2p21, 16q22 and 3q13, respectively). (PMID: 16098809) [HMDB]