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Metabolic Modeling Tutorial
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MetaCyc Reaction: 2.4.2.1/2.4.2.15

Superclasses: Reactions Classified By Conversion Type Simple Reactions Chemical Reactions
Reactions Classified By Substrate Small-Molecule Reactions

EC Number: 2.4.2.1 , 2.4.2.15

Enzymes and Genes:
xanthosine phosphorylase Inferred from experiment : xapA ( Escherichia coli K-12 substr. MG1655 )
guanosine phosphorylase Inferred from experiment ( Oryctolagus cuniculus )
purine nucleoside phosphorylase Inferred from experiment : PNP ( Homo sapiens )
purine nucleoside phosphorylase : PNP ( Plasmodium falciparum )
purine nucleoside phosphorylase Inferred from experiment : deoD ( Escherichia coli K-12 substr. MG1655 )

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

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 (2.4.2.1)

Enzyme Commission Primary Name for 2.4.2.1: purine-nucleoside phosphorylase

Enzyme Commission Synonyms for 2.4.2.1: 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 2.4.2.15: guanosine phosphorylase

Standard Gibbs Free Energy (ΔrG in kcal/mol): 0.730011 Inferred by computational analysis [Latendresse13]

Summary:
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 2.4.2.15) describes this specific reaction, the E. coli enzyme has been associated with this reaction, since EC 2.4.2.15 was defined for a much more specific rabbit bone marrow enzyme [Yamada61].

Enzyme Commission Summary for 2.4.2.1:
Specificity not completely determined. Can also catalyse ribosyltransferase reactions of the type catalysed by EC 2.4.2.5, nucleoside ribosyltransferase.

Enzyme Commission Summary for 2.4.2.15:
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 2.4.2.1, (guanosine + phosphate ↔ guanine + α-D-ribose-1-phosphate).

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

Gene-Reaction Schematic: ?

Instance reactions of [a purine ribonucleoside + phosphate ↔ a purine base + α-D-ribose-1-phosphate] (2.4.2.1):
i1: adenosine + phosphate ↔ adenine + α-D-ribose-1-phosphate (2.4.2.1)

i2: guanosine + phosphate ↔ guanine + α-D-ribose-1-phosphate (2.4.2.1/2.4.2.15)
i3: inosine + phosphate ↔ hypoxanthine + α-D-ribose-1-phosphate (2.4.2.1)

Unification Links: KEGG:R02147 , Rhea:13233

Relationship Links: BRENDA:EC:2.4.2.1 , BRENDA:EC:2.4.2.15 , ENZYME:EC:2.4.2.1 , ENZYME:EC:2.4.2.15 , IUBMB-ExplorEnz:EC:2.4.2.1 , IUBMB-ExplorEnz:EC:2.4.2.15


References

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

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 MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
Page generated by SRI International Pathway Tools version 18.5 on Thu Dec 18, 2014, BIOCYC13A.