This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
|Superclasses:||Biosynthesis → Nucleosides and Nucleotides Biosynthesis → Purine Nucleotide Biosynthesis → Purine Nucleotide Salvage → Guanine and Guanosine Salvage|
Guanosine nucleotides can be synthesized de novo. In that route GMP (GMP) is synthesized via IMP (IMP) and XMP (XMP) , which is converted to GMP by the action of GMP synthetase, an enzyme that can use either glutamine or ammonia as substrate (see superpathway of guanosine nucleotides de novo biosynthesis II). Note that the free base guanine or the ribonucleoside guanosine are not produced via the de novo pathway.
Many organisms can also recycle guanosine nucleotides by a combination of degradation and salvage pathways. The degradation pathway is responsible for the degradation of the nucleotides to the nucleoside guanosine and the base guanine, which can be further degraded via xanthine and urate, and eventually catabolized to basic building blocks (see superpathway of guanosine nucleotides degradation (plants)).
The enzyme purine phosphorylase (DeoD) (EC 22.214.171.124) cleaves guanosine to guanine and α-D-ribose-1-phosphate, while a second enzyme, such as xanthine-guanine phosphoribosyltransferase, can utilize 5-phospho-α-D-ribose 1-diphosphate to convert the free base to the mononucleotide GMP.
Either of these routes enables the organism to salvage the degradation products of guanosine nucleotides, and recycle them back to nucleotide form.
Unification Links: EcoCyc:PWY-6620
HammerJespersen71: Hammer-Jespersen K, Munch-Petersen A, Schwartz M, Nygaard P (1971). "Induction of enzymes involed in the catabolism of deoxyribonucleosides and ribonucleosides in Escherichia coli K 12." Eur J Biochem 1971;19(4);533-8. PMID: 4931185
Lewis79: Lewis AS, Lowy BA (1979). "Human erythrocyte purine nucleoside phosphorylase: molecular weight and physical properties. A Theorell-Chance catalytic mechanism." J Biol Chem 254(19);9927-32. PMID: 114517
Liu83: Liu SW, Milman G (1983). "Purification and characterization of Escherichia coli guanine-xanthine phosphoribosyltransferase produced by a high efficiency expression plasmid utilizing a lambda PL promoter and CI857 temperature-sensitive repressor." J Biol Chem 1983;258(12);7469-75. PMID: 6305942
Xu97b: Xu Y, Eads J, Sacchettini JC, Grubmeyer C (1997). "Kinetic mechanism of human hypoxanthine-guanine phosphoribosyltransferase: rapid phosphoribosyl transfer chemistry." Biochemistry 36(12);3700-12. PMID: 9132023
Balendiran99: Balendiran GK, Molina JA, Xu Y, Torres-Martinez J, Stevens R, Focia PJ, Eakin AE, Sacchettini JC, Craig SP (1999). "Ternary complex structure of human HGPRTase, PRPP, Mg2+, and the inhibitor HPP reveals the involvement of the flexible loop in substrate binding." Protein Sci 8(5);1023-31. PMID: 10338013
Bennett03: Bennett EM, Li C, Allan PW, Parker WB, Ealick SE (2003). "Structural basis for substrate specificity of Escherichia coli purine nucleoside phosphorylase." J Biol Chem 278(47);47110-8. PMID: 12937174
Bennett03a: Bennett EM, Anand R, Allan PW, Hassan AE, Hong JS, Levasseur DN, McPherson DT, Parker WB, Secrist JA, Sorscher EJ, Townes TM, Waud WR, Ealick SE (2003). "Designer gene therapy using an Escherichia coli purine nucleoside phosphorylase/prodrug system." Chem Biol 10(12);1173-81. PMID: 14700625
Bertoša14: Bertosa B, Mikleusevic G, Wielgus-Kutrowska B, Narczyk M, Hajnic M, Lescic Asler I, Tomic S, Luic M, Bzowska A (2014). "Homooligomerization is needed for stability: a molecular modelling and solution study of Escherichia coli purine nucleoside phosphorylase." FEBS J 281(7);1860-71. PMID: 24785777
Bezirdzhian86: Bezirdzhian KhO, Kocharian ShM, Akopian ZhI (1986). "[Isolation of the hexameric form of purine nucleoside phosphorylase from E. coli. Comparative study of trimeric and hexameric forms of the enzyme]." Biokhimiia 1986;51(7);1085-92. PMID: 3089333
Bezirdzhian87: Bezirdzhian KhO, Kocharian ShM, Akopian ZhI (1987). "[Hexamere purine nucleoside phosphorylase from Escherichia coli K-12. Kinetic analysis and mechanism of reaction]." Biokhimiia 52(11);1770-6. PMID: 3125860
Bezirdzhian87a: Bezirdzhian KhO, Kocharian ShM, Akopian ZhI (1987). "[Hexameric purine nucleoside phosphorylase II from Escherichia coli K-12. Physico-chemical and catalytic properties and stabilization with substrates]." Biokhimiia 1987;52(10);1624-31. PMID: 3122852
Buxton75: Buxton RS (1975). "Genetic analysis of thymidine-resistant and low-thymine-requiring mutants of Escherichia coli K-12 induced by bacteriophage Mu-1." J Bacteriol 121(2);475-84. PMID: 1089630
Buxton80: Buxton RS, Hammer-Jespersen K, Valentin-Hansen P (1980). "A second purine nucleoside phosphorylase in Escherichia coli K-12. I. Xanthosine phosphorylase regulatory mutants isolated as secondary-site revertants of a deoD mutant." Mol Gen Genet 179(2);331-40. PMID: 7007808
Bzowska88: Bzowska A, Kulikowska E, Darzynkiewicz E, Shugar D (1988). "Purine nucleoside phosphorylase. Structure-activity relationships for substrate and inhibitor properties of N-1-, N-7-, and C-8-substituted analogues; differentiation of mammalian and bacterial enzymes with N-1-methylinosine and guanosine." J Biol Chem 263(19);9212-7. PMID: 3132457
Dandanell05: Dandanell G, Szczepanowski RH, Kierdaszuk B, Shugar D, Bochtler M (2005). "Escherichia coli purine nucleoside phosphorylase II, the product of the xapA gene." J Mol Biol 348(1);113-25. PMID: 15808857
Deo85: Deo SS, Tseng WC, Saini R, Coles RS, Athwal RS (1985). "Purification and characterization of Escherichia coli xanthine-guanine phosphoribosyltransferase produced by plasmid pSV2gpt." Biochim Biophys Acta 839(3);233-9. PMID: 3886014
DiazMejia09: Diaz-Mejia JJ, Babu M, Emili A (2009). "Computational and experimental approaches to chart the Escherichia coli cell-envelope-associated proteome and interactome." FEMS Microbiol Rev 33(1);66-97. PMID: 19054114
Ding10: Ding QB, Ou L, Wei DZ, Wei XK, Xu YM, Zhang CY (2010). "Enzymatic synthesis of nucleosides by nucleoside phosphorylase co-expressed in Escherichia coli." J Zhejiang Univ Sci B 11(11);880-8. PMID: 21043057
Dong14: Dong WR, Sun CC, Zhu G, Hu SH, Xiang LX, Shao JZ (2014). "New function for Escherichia coli xanthosine phophorylase (xapA): genetic and biochemical evidences on its participation in NAD(+) salvage from nicotinamide." BMC Microbiol 14;29. PMID: 24506841
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