PathwayStep2252 PathwayStep2261 PathwayStep2279 Pyrimidine biosynthesis Pyrimidine salvage reactions Pyrimidine catabolism Pyrimidine metabolism Authored: D'Eustachio, P, 2003-10-25 14:57:00 Edited: D'Eustachio, P, 0000-00-00 00:00:00 GENE ONTOLOGYGO:0006206 Pubmed16098809 Reactome Database ID Release 4373848 Reactome, http://www.reactome.org ReactomeREACT_957 Reviewed: Graves, L, Rush, MG, 0000-00-00 00:00:00 The events of human pyrimidine metabolism are conveniently, if somewhat arbitrarily, grouped into four pathways: de novo synthesis of the pyrimidine ring and its conversion to uridine 5'-monophosphate (UMP), the biosynthesis of other pyrimidine ribo- and deoxyribonucleotides, pyrimidine salvage reactions, and pyrimidine catabolism (Loffler et al. 2005).<P><B>De novo synthesis of the pyrimidine ring and its conversion to UMP.</B> The pyrimidine base orotate is synthesized from glutamine, bicarbonate, and aspartate. Orotate reacts with 5-phospho-alpha-D-ribose 1-diphosphate (PRPP) and is then decarboxylated to form the pyrimidine nucleotide UMP.<P><B>Pyrimidine biosynthesis [interconversion].</B> Pyrimidine ribo- and deoxyribonucleotide di- and triphosphates are synthesized, both from UMP and from pyrimidine ribonucleotide monophosphates generated in salvage reactions. <P><B>Pyrimidine salvage reactions.</B> Pyrimidine nucleosides and free bases generated by DNA and RNA breakdown are converted to nucleotide monophosphates.<P><B>Pyrimidine catabolism.</B> The pyrimidine bases thymine and uracil are degraded to beta-aminoisobutyrate and beta-alanine, respectively, which are excreted from the body.