(R)-3-aminoisobutyric acid + pyruvate => 2-methyl-3-oxopropanoate + alanine conversion of 3-Ureidoiosbutyrate to 3-Aminoisobutyrate Mitochondrial uptake of (R)-3-aminoisobutyric acid reduction of thymine to form 5,6-Dihydrothymine 5,6-dihydrothymine + H2O => beta-ureidoisobutyrate Mitochondrial uptake of beta-alanine beta-alanine + pyruvate => 3-oxopropanoate + alanine TMP, (d)UMP, uridine 2' monophosphate, or uridine 3'-monophosphate + H2O => thymidine, deoxyuridine, or uridine + orthophosphate [NT5M] TMP, uridine 2', 3', or 5' monophosphates, or deoxyuridine 3' or 5' monophosphates + H2O => thymidine or (deoxy)uridine + orthophosphate [NT5C] (d)CMP, TMP, or (d)UMP + H2O => (deoxy)cytidine, thymidine, or (deoxy)uridine + orthophosphate [NT5C1A] (d)CMP, TMP, or (d)UMP + H2O => (deoxy)cytidine, thymidine, or (deoxy)uridine + orthophosphate [NT5C3] CMP or TMP or UMP + H2O => cytidine, thymidine, or uridine + orthophosphate [NT5E] reduction of uracil to form dihydrouracil 5,6-dihydrouracil + H2O => beta-ureidopropionate (deoxy)uridine + orthophosphate <=> uracil + (deoxy)ribose 1-phosphate [UPP] thymidine or deoxyuridine + orthophosphate <=> thymine or uracil + 2-deoxy-D-ribose 1-phosphate [TYMP] conversion of 3-ureidopropionate to beta-alanine PathwayStep2262 PathwayStep2263 PathwayStep2264 PathwayStep2265 PathwayStep2266 PathwayStep2276 PathwayStep2277 PathwayStep2274 PathwayStep2275 PathwayStep2272 PathwayStep2273 PathwayStep2270 PathwayStep2271 PathwayStep2269 PathwayStep2268 PathwayStep2267 PathwayStep2278 Pyrimidine catabolism Authored: Jassal, B, 2003-06-17 09:00:26 GENE ONTOLOGYGO:0046135 ISBN0079130356 In parallel sequences of three reactions each, thymine is converted to beta-aminoisobutyrate and uracil is converted to beta-alanine. Both of these molecules are excreted in human urine and appear to be normal end products of pyrimidine catabolism (Griffith 1986; Webster et al. 2001). Mitochondrial AGXT2, however, can also catalyze the transamination of both molecules with pyruvate, yielding 2-oxoacids that can be metabolized further by reactions of branched-chain amino acid and short-chain fatty acid catabolism (Tamaki et al. 2000). The importance of these reactions in normal human pyrimidine catabolism has not been well worked out. Pubmed10989446 Pubmed3090932 Reactome Database ID Release 4373621 Reactome, http://www.reactome.org ReactomeREACT_1023