(d)GDP + ADP <=> (d)GMP + ATP [GUK1] (d)CMP or UMP + ATP <=> (d)CDP or UDP + ADP [CMPK1] (d)CDP or UDP + ADP <=> (d)CMP or UMP + ATP [CMPK1] phosphorylation of dUMP or TMP to dUDP or TDP dUDP or TDP + ADP <=> dUMP or TMP + ATP [DTYMK] UTP + glutamine + ATP + H2O => CTP + glutamate + ADP + orthophosphate [CTPS] ADP + ADP <=> AMP + ATP [AK2] (d)AMP or (d)CMP + ATP <=> (d)ADP or (d)CDP + ADP [AK5] (d)ADP or (d)CDP + ADP <=> (d)AMP or (d)CMP + ATP [AK5] (d)GMP + ATP <=> (d)GDP + ADP [GUK1] (d)NDP + ATP <=> (d)NTP + ADP [NME1,2,3] regeneration of active (reduced) Thioredoxin thioredoxin, reduced (cytosol) <=> thioredoxin, reduced (nucleus) glutathione (oxidized) + NADPH + H+ => 2 glutathione (reduced) + NADP+ thioredoxin, oxidized (nucleus) <=> thioredoxin, oxidized (cytosol) NDP + reduced thioredoxin => dNDP + oxidized thioredoxin + H2O glutaredoxin (oxidized) + glutathione (reduced) => glutaredoxin (reduced) + glutathione (oxidized) NDP + reduced glutaredoxin => dNDP + oxidized glutaredoxin + H2O NDP + reduced thioredoxin => dNDP + oxidized thioredoxin + H2O UTP + glutamine + ATP + H2O => CTP + glutamate + ADP + orthophosphate [CTPS2] (d)NTP + ADP <=> (d)NDP + ATP [NME4] (d)NTP + ADP <=> (d)NDP + ATP [NME1,2,3] (d)NDP + ATP <=> (d)NTP + ADP [NME4] AMP + ATP <=> ADP + ADP [AK2] (d)ADP + ADP <=> (d)AMP + ATP [AK1] (d)AMP + ATP <=> (d)ADP + ADP [AK1] PathwayStep2301 PathwayStep2300 PathwayStep2303 PathwayStep2302 PathwayStep2305 PathwayStep2304 PathwayStep2306 PathwayStep2285 PathwayStep2286 PathwayStep2287 PathwayStep2288 PathwayStep2281 PathwayStep2282 PathwayStep2283 PathwayStep2284 PathwayStep2291 PathwayStep2290 PathwayStep2295 PathwayStep2294 PathwayStep2293 PathwayStep2292 PathwayStep2299 PathwayStep2298 PathwayStep2297 PathwayStep2296 PathwayStep2289 Synthesis and interconversion of nucleotide di- and triphosphates An array of kinases catalyze the reversible phosphorylation of nucleotide monophosphates to form nucleotide diphosphates and triphosphates.<p>Nucleoside monophosphate kinases catalyze the reversible phosphorylation of nucleoside and deoxynucleoside 5'-monophosphates to form the corresponding nucleoside 5'-diphosphates. Most appear to have restricted specificities for nucleoside monophosphates, and to use ATP preferentially (Van Rompay et al. 2000; Anderson 1973; Noda 1973). The total number of human enzymes that catalyze these reactions in vivo is not clear. In six cases, a well-defined biochemical activity has been associated with a purified protein, and these are annotated here. However, additional nucleoside monophosphate kinase-like human proteins have been identified in molecular cloning studies whose enzymatic activities are unknown, and several distinctive nucleoside monophosphate kinase activities detected in cell extracts, e.g., a GTP-requiring adenylate kinase activity (Wilson et al. 1976) and one or more guanylate kinase activities (Jamil et al. 1975) have not been unambiguously associated with specific human proteins.<P>The nucleoside monophosphates against which each of the six well-characterized enzymes is active is shown in the table (Van Rompay et al. 2000). All six efficiently use ATP as a phosphate donor, but have some activity with other nucleoside triphosphates as well in vitro. The high concentrations of ATP relative to other nucleoside triphosphates in vivo makes it the likely major phosphate donor in these reactions under most conditions.<P>All of these phosphorylation reactions are freely reversible in vitro when carried out with purified enzymes and substrates, having equilibrium constants near 1. In vivo, high ratios of ATP to ADP are likely to favor the forward direction of these reactions, i.e., the conversion of (d)NMP and ATP to (d)NDP and ADP. At the same time, the reversibility of the reactions and the overlapping substrate specificities of the enzymes raises the possibility that this group of reactions can buffer the intracellular nucleotide pool and regulate the relative concentrations of individual nucleotides in the pool: if any one molecule builds up to unusually high levels, multiple routes appear to be open not only to dispose of it but to use it to increase the supply of less abundant nucleotides.<p>Ribonucleotide reductase catalyzes the synthesis of deoxyribonucleotide diphosphates from ribonucleotide diphosphates. Authored: D'Eustachio, P, 2010-02-05 Edited: D'Eustachio, P, 2010-02-05 GENE ONTOLOGYGO:0015949 ISBN0121227022 Pubmed11008000 Pubmed177353 Pubmed5940 Reactome Database ID Release 43499943 Reactome, http://www.reactome.org ReactomeREACT_21330 Reviewed: Graves, L, Rush, MG, 0000-00-00 00:00:00