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|
Some taxa known to possess this pathway include : Escherichia coli K-12 substr. MG1655
Purine bases consist of a six-membered and a five-membered nitrogen-containing rings fused together. There are four purine bases, namely adenine, guanine, hypoxanthine and xanthine. Purine nucleotides may be synthesized de novo from simpler precursors, or they may be derived from exogenous purine nucleosides and bases by the salvage pathways.
In Escherichia coli, the salvage pathways collect exogenous, preformed bases and nucleosides for nucleotide synthesis, reutilize bases and nucleosides produced endogenously from nucleotide turnover, and make available the pentose moieties of exogenous nucleosides as sources of carbon. When free bases or nucleosides present in the growth medium are salvaged, the contribution from the de novo pathways to nucleotide synthesis is greatly suppressed.
About This Pathway
Xanthosine is converted to xanthine by xanthosine phosphorylase, one of the two purine nucleoside phosphorylases (PNPs) in Escherichia coli, encoded by the xapA gene [Seeger95, Dandanell05]. This enzyme does not cleave or synthesize adenosine and deoxyadenosine but catalyzes the phosphorolysis of xanthosine, inosine and guanosine with comparable efficiency.
Unification Links: EcoCyc:SALVPURINE2-PWY
Martha Arnaud on Tue Jan 21, 2003:
The pathways "salvage pathways of guanine, xanthine, and their nucleosides" and "salvage pathways of adenine, hypoxanthine, and their nucleotides" supersede the pathway formerly called "purine ribonucleotide/ribonucleoside metabolism."
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
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
Seeger95: Seeger C, Poulsen C, Dandanell G (1995). "Identification and characterization of genes (xapA, xapB, and xapR) involved in xanthosine catabolism in Escherichia coli." J Bacteriol 177(19);5506-16. PMID: 7559336
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). "[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
Bezirdzhian87a: 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
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
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
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
Guddat02: Guddat LW, Vos S, Martin JL, Keough DT, de Jersey J (2002). "Crystal structures of free, IMP-, and GMP-bound Escherichia coli hypoxanthine phosphoribosyltransferase." Protein Sci 11(7);1626-38. PMID: 12070315
HammerJespersen80: Hammer-Jespersen K, Buxton RS, Hansen TD (1980). "A second purine nucleoside phosphorylase in Escherichia coli K-12. II. Properties of xanthosine phosphorylase and its induction by xanthosine." Mol Gen Genet 1980;179(2);341-8. PMID: 7007809
Khersonsky11: Khersonsky O, Malitsky S, Rogachev I, Tawfik DS (2011). "Role of chemistry versus substrate binding in recruiting promiscuous enzyme functions." Biochemistry 50(13);2683-90. PMID: 21332126
Kocharian86: Kocharian ShM, Melkumian MA (1986). "[Genetic analysis of Escherichia coli K-12 mutants defective for the structural and regulatory genes for second purine nucleoside phosphorylase]." Genetika 22(8);2055-65. PMID: 3095187
Konrad12: Konrad A, Piškur J, Liberles DA (2012). "The evolution of catalytic residues and enzyme mechanism within the bacterial nucleoside phosphorylase superfamily 1." Gene 510(2);154-61. PMID: 22967797
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