|Superclasses:||Reactions Classified By Conversion Type → Simple Reactions → Chemical Reactions|
|Reactions Classified By Substrate → Small-Molecule Reactions|
Enzymes and Genes:
xanthosine phosphorylase : xapA ( Escherichia coli K-12 substr. MG1655 )
guanosine phosphorylase ( Oryctolagus cuniculus )
purine nucleoside phosphorylase : PNP ( Homo sapiens )
purine nucleoside phosphorylase : PNP ( Plasmodium falciparum )
purine nucleoside phosphorylase : deoD ( Escherichia coli K-12 substr. MG1655 )
The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, 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 (126.96.36.199)
Enzyme Commission Primary Name for 188.8.131.52: purine-nucleoside phosphorylase
Enzyme Commission Synonyms for 184.108.40.206: inosine phosphorylase, PNPase, PUNPI, PUNPII, inosine-guanosine phosphorylase, nucleotide phosphatase, purine deoxynucleoside phosphorylase, purine deoxyribonucleoside phosphorylase, purine nucleoside phosphorylase, purine ribonucleoside phosphorylase
Enzyme Commission Primary Name for 220.127.116.11: guanosine phosphorylase
Standard Gibbs Free Energy (ΔrG'° in kcal/mol): 0.730011 [Latendresse13]
This is a specific case of the non-specific reaction catalyzed by purine-nucleoside phosphorylase a purine ribonucleoside + phosphate ↔ a purine base + α-D-ribose-1-phosphate.
Even though a different EC reaction (EC 18.104.22.168) describes this specific reaction, the E. coli enzyme has been associated with this reaction, since EC 22.214.171.124 was defined for a much more specific rabbit bone marrow enzyme [Yamada61].
Enzyme Commission Summary for 126.96.36.199:
Specificity not completely determined. Can also catalyse ribosyltransferase reactions of the type catalysed by EC 188.8.131.52, nucleoside ribosyltransferase.
Enzyme Commission Summary for 184.108.40.206:
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 220.127.116.11, (guanosine + phosphate ↔ guanine + α-D-ribose-1-phosphate).
Instance reactions of [a purine ribonucleoside + phosphate ↔ a purine base + α-D-ribose-1-phosphate] (18.104.22.168):
i1: adenosine + phosphate ↔ adenine + α-D-ribose-1-phosphate (22.214.171.124)
i2: guanosine + phosphate ↔ guanine + α-D-ribose-1-phosphate (126.96.36.199/188.8.131.52)
i3: inosine + phosphate ↔ hypoxanthine + α-D-ribose-1-phosphate (184.108.40.206)
Saunders69: Saunders PP, Wilson BA, Saunders GF (1969). "Purification and comparative properties of a pyrimidine nucleoside phosphorylase from Bacillus stearothermophilus." J Biol Chem 244(13);3691-7. PMID: 4978445
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