MetaCyc Reaction:

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

EC Number:

Enzymes and Genes:

Escherichia coli K-12 substr. MG1655: purine nucleoside phosphorylaseInferred from experiment: deoD
Homo sapiens: purine nucleoside phosphorylaseTraceable author statement to experimental support: PNP

In Pathway: purine deoxyribonucleosides degradation I, purine deoxyribonucleosides degradation II

Note that this reaction equation differs from the official Enzyme Commission reaction equations for this EC number, which can be found here and here .

The direction shown, i.e. which substrates are on the left and right sides, is in accordance with the direction in which it was curated.

Mass balance status: Balanced.

Direct generic reaction:
a purine 2'-deoxyribonucleoside + phosphate = a purine base + 2-deoxy-α-D-ribose 1-phosphate (

Enzyme Commission Primary Name: purine-nucleoside phosphorylase

Enzyme Commission Synonyms: inosine phosphorylase, PNPase, PUNPI, PUNPII, inosine-guanosine phosphorylase, nucleotide phosphatase, purine deoxynucleoside phosphorylase, purine deoxyribonucleoside phosphorylase, purine nucleoside phosphorylase, purine ribonucleoside phosphorylase

Standard Gibbs Free Energy (ΔrG in kcal/mol): -7.9499817Inferred by computational analysis [Latendresse13]

Enzyme Commission Summary:
Specificity not completely determined. Can also catalyse ribosyltransferase reactions of the type catalysed by EC, nucleoside ribosyltransferase.

Citations: [Agarwal69 , Heppel52, Saunders69, Tsuboi57, Friedkin61, Kalckar47]

Gene-Reaction Schematic

Gene-Reaction Schematic

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

i2: inosine + phosphate ↔ hypoxanthine + α-D-ribose-1-phosphate (

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

Unification Links: KEGG:R01969, Rhea:27738

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


Agarwal69: Agarwal RP, Parks RE (1969). "Purine nucleoside phosphorylase from human erythrocytes. IV. Crystallization and some properties." J Biol Chem 244(4);644-7. PMID: 5768862

Friedkin61: Friedkin M, Kalckar H (1961). "Nucleoside phosphorylases." In: Boyer, P.D., Lardy, H. and Myrbäck, K. (Eds), The Enzymes, 2nd edn, vol. 5, Academic Press, New York, pp. 237-255.

Heppel52: Heppel LA, Hilmoe RJ (1952). "[Phosphorolysis and hydrolysis of purine ribosides by enzymes from yeast]." J Biol Chem 198(2);683-94. PMID: 12999785

Kalckar47: Kalckar HM (1947). "The enzymatic synthesis of purine ribosides." J. Biol. Chem. 167 477-486.

Latendresse13: Latendresse M. (2013). "Computing Gibbs Free Energy of Compounds and Reactions in MetaCyc."

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

Tsuboi57: Tsuboi KK, Hudson PB (1957). "Enzymes of the human erythrocyte. I. Purine nucleoside phosphorylase; isolation procedure." J Biol Chem 224(2);879-87. PMID: 13405917

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Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
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