Escherichia coli K-12 substr. MG1655 Reaction:

Superclasses: Reactions Classified By Conversion TypeSimple ReactionsChemical Reactions
Reactions Classified By SubstrateSmall-Molecule Reactions

EC Number:

Enzymes and Genes:
xanthosine phosphorylaseInferred from experiment: xapA
purine nucleoside phosphorylaseInferred from experiment: deoD

In Pathway: guanine and guanosine salvage, guanosine nucleotides degradation III, purine ribonucleosides degradation

The direction shown, i.e. which substrates are on the left and right sides, is in accordance with the Enzyme Commission system.

Mass balance status: Balanced.

Direct generic reaction:
a purine ribonucleoside + phosphate ↔ a purine base + α-D-ribose-1-phosphate (

Enzyme Commission Primary Name: guanosine phosphorylase

Enzyme Commission Summary:
This enzyme has been defined based on a single publication of an enzyme from rabbit bone marrow that appears to be highly specific for guanosine and deoxyguanosine [Yamada61]. Most enzymes that are known to catalyze this reaction, such as the human purine nucleoside phosphorylase, can accept other purines as well, and thus were attributed to a specific case of the more general enzyme EC, ( guanosine + phosphate ↔ guanine + α-D-ribose-1-phosphate).

Gene-Reaction Schematic

Gene-Reaction Schematic

Instance reactions of [a purine ribonucleoside + phosphate ↔ a purine base + α-D-ribose-1-phosphate] (
i1: inosine + phosphate ↔ α-D-ribose-1-phosphate + hypoxanthine (

i2: guanosine + phosphate ↔ α-D-ribose-1-phosphate + guanine (
i3: adenosine + phosphate ↔ α-D-ribose-1-phosphate + adenine (

Relationship Links: BRENDA:EC:, ENZYME:EC:, IUBMB-ExplorEnz:EC:


Yamada61: Yamada, E.W. (1961). "The phosphorolysis of nucleosides by rabbit bone marrow." J Biol Chem 236;3043-6. PMID: 14008731

Report Errors or Provide Feedback
Please cite the following article in publications resulting from the use of EcoCyc: Nucleic Acids Research 41:D605-12 2013
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