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MetaCyc Enzyme: purine nucleoside phosphorylase

Gene: PNP Accession Number: HS02151 (MetaCyc)

Synonyms: NP

Species: Homo sapiens

Subunit composition of purine nucleoside phosphorylase = [PNP]3
         purine nucleoside phosphorylase subunit = PNP

Summary:
The human purine nucleoside phosphorylase (PNP) catalyzes the reversible phosphorolysis of the purine nucleosides and deoxynucleosides inosine, guanosine, deoxyinosine and deoxyguanosine [Zannis78, Williams84]. Arsenate being chemically similar to phosphate can substitute for phosphate resulting in the formation of ribose-1-arsenate [Radabaugh02]. The 6-aminopurine nucleosides, adenosine and 2'-deoxyadenosine are not natural substrates for mammalian purine nucleoside phosphorylase, unlike prokaryotic purine nucleoside phosphorylase [Stoychev02].

On the basis of structural studies, two families of purine nucleoside phosphorylases have been proposed. Nucleoside phosphorylase-1 enzymes are trimeric or tetrameric with a single domain subunit. Nucleoside phosphorylase-2 enzymes are dimeric and have a two-domain subunit [Pugmire02]. The native human erythrocyte purine nucleoside phosphorylase is a homotrimer [Ealick90]. The subunits of the native enzyme showed isoelectric heterogeneity [Zannis78, Lewis79].

The enzyme functions in the direction of phosphorolysis in mammalian purine degradation via coupling with guanine deaminase and xanthine oxidase in guanosine nucleotides degradation III. It also produces purine substrates used by hypoxanthine-guanine phosphoribosyltransferase in guanine and guanosine salvage.

High purine nucleoside phosphorylase activity is found in human erythrocytes, peripheral lymphocytes, granulocytes and in the kidney. A deficiency of the enzyme in humans is associated with immunodeficiency due to impairment of T-cell function. In addition, the human enzyme is a target for drug development to treat conditions of abnormal T-cell activation [Silva03][Bzowska00].

Map Position: [14,725,032 -> 14,732,705]

Molecular Weight of Polypeptide: 32.118 kD (from nucleotide sequence), 32 kD (experimental)

Molecular Weight of Multimer: 93.8 kD (experimental) [Zannis78]

Unification Links: ArrayExpress:P00491 , Entrez-gene:4860 , Entrez-Nucleotide:J02672 , Entrez-Nucleotide:M13951 , Entrez-Nucleotide:M13952 , Entrez-Nucleotide:M13953 , Entrez-Nucleotide:X00737 , Entrez:AAA36460 , Entrez:CAA25320 , GeneCards:NP , ModBase:P00491 , MOPED:P00491 , OMIM:164050 , PDB:1ULA , PDB:1ULB , RefSeq:NM_000270 , RefSeq:NP_000261 , Swiss-Model:P00491 , UCSC Human Genome:NM_000270 , UniGene:75514 , UniProt:P00491

Relationship Links: PDB:Structure:1M73 , PDB:Structure:1PF7 , PDB:Structure:1PWY , PDB:Structure:1RCT , PDB:Structure:1RFG , PDB:Structure:1RR6 , PDB:Structure:1RSZ , PDB:Structure:1RT9 , PDB:Structure:1ULA , PDB:Structure:1ULB , PDB:Structure:1V2H , PDB:Structure:1V3Q , PDB:Structure:1V41 , PDB:Structure:1V45 , PDB:Structure:1YRY , PDB:Structure:2A0W , PDB:Structure:2A0X , PDB:Structure:2A0Y

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: inosine + phosphate ↔ hypoxanthine + α-D-ribose-1-phosphate (2.4.2.1)

GO Terms:

Biological Process: GO:0006139 - nucleobase-containing compound metabolic process
GO:0006304 - DNA modification
Molecular Function: GO:0004645 - phosphorylase activity
GO:0004731 - purine-nucleoside phosphorylase activity
GO:0016757 - transferase activity, transferring glycosyl groups

Credits:
Revised 14-Oct-2009 by Fulcher CA , SRI International


Enzymatic reaction of: deoxyinosine phosphorylase (purine nucleoside phosphorylase)

2'-deoxyinosine + phosphate <=> hypoxanthine + 2-deoxy-α-D-ribose 1-phosphate

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the direction in which it was curated.

This reaction is reversible.

In Pathways: purine deoxyribonucleosides degradation

Credits:
Imported from HumanCyc 05-Jun-2014 by Weerasinghe D , SRI International


Enzymatic reaction of: deoxyguanosine phosphorylase (purine nucleoside phosphorylase)

2'-deoxyguanosine + phosphate <=> guanine + 2-deoxy-α-D-ribose 1-phosphate

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the direction in which it was curated.

This reaction is reversible.

In Pathways: purine deoxyribonucleosides degradation

Credits:
Imported from HumanCyc 05-Jun-2014 by Weerasinghe D , SRI International


Enzymatic reaction of: xanthosine phosphorylase (purine nucleoside phosphorylase)

xanthosine + phosphate <=> α-D-ribose-1-phosphate + xanthine

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the direction of enzyme catalysis.

This reaction is reversible. [Stoychev02]

In Pathways: purine nucleotides degradation II (aerobic) , urate biosynthesis/inosine 5'-phosphate degradation , purine ribonucleosides degradation

Summary:
At pH 5.7 the Km for xanthosine was 508 μM and at pH 6.5 the Km for xanthosine was 1600 μM. These values are significantly higher than the Km for guanosine of 91 μM at pH 5.7 and the Km for guanosine of 14 μM at pH 6.5 [Stoychev02].


Enzymatic reaction of: guanosine phosphorylase (purine nucleoside phosphorylase)

EC Number: 2.4.2.15

guanosine + phosphate <=> guanine + α-D-ribose-1-phosphate

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the direction of enzyme catalysis.

This reaction is reversible. [Lewis79]

Alternative Substrates for guanosine: 2'-deoxyguanosine [Lewis79 ]

In Pathways: purine nucleotides degradation II (aerobic) , superpathway of purine nucleotide salvage , guanosine nucleotides degradation III , guanine and guanosine salvage , purine ribonucleosides degradation

Summary:
This enzyme catalyzes cleavage of the glycosidic bond of purine ribonucleosides (and also of purine deoxyribonucleosides) in the presence of phosphate which acts as a second substrate, producing the purine base and α-D-ribose-1-phosphate. This phosphorolysis is reversible with the natural substrates of the enzyme (reviewed in [Bzowska00]).

Unlike the prokaryotic enzyme, adenosine is not a natural substrate for mammalian purine nucleoside phosphorylase (in [Stoychev02]). xanthosine has been shown to be a substrate for phosphorolysis by mammalian purine nucleoside phosphorylase, but it had a higher Km than guanosine at the pHs tested [Stoychev02] and reviewed in [Kulikowska04].

Kinetic Parameters:

Substrate
Km (μM)
Citations
guanosine
44.3
[Lewis79]


Enzymatic reaction of: inosine phosphorylase (purine nucleoside phosphorylase)

inosine + phosphate <=> hypoxanthine + α-D-ribose-1-phosphate

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the direction of enzyme catalysis.

This reaction is reversible. [Lewis79]

In Pathways: purine nucleotides degradation II (aerobic) , adenine and adenosine salvage III , adenosine nucleotides degradation II , purine ribonucleosides degradation

Summary:
This enzyme catalyzes cleavage of the glycosidic bond of purine ribonucleosides (and also of purine deoxyribonucleosides) in the presence of phosphate which acts as a second substrate, producing the purine base and α-D-ribose-1-phosphate. This phosphorolysis is reversible with the natural substrates of the enzyme (reviewed in [Bzowska00]).

Unlike the prokaryotic enzyme, adenosine is not a natural substrate for mammalian purine nucleoside phosphorylase (in [Stoychev02]). xanthosine has been shown to be a substrate for phosphorolysis by mammalian purine nucleoside phosphorylase, but it had a higher Km than guanosine at the pHs tested [Stoychev02] and reviewed in [Kulikowska04].

Kinetic Parameters:

Substrate
Km (μM)
Citations
inosine
50.0
[Lewis79]


Enzymatic reaction of: purine-nucleoside:phosphate ribosyltransferase (purine nucleoside phosphorylase)

a purine ribonucleoside + phosphate <=> a purine base + α-D-ribose-1-phosphate

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the Enzyme Commission system.

This reaction is reversible.

In Pathways: purine nucleotides degradation II (aerobic) , adenosine nucleotides degradation II , superpathway of purine nucleotide salvage , adenine and adenosine salvage III , adenine and adenosine salvage I , purine ribonucleosides degradation

Summary:
This enzyme catalyzes cleavage of the glycosidic bond of purine ribonucleosides (and also of purine deoxyribonucleosides) in the presence of phosphate which acts as a second substrate, producing the purine base and α-D-ribose-1-phosphate. This phosphorolysis is reversible with the natural substrates of the enzyme (reviewed in [Bzowska00]).


Enzymatic reaction of: arsenate reductase (purine nucleoside phosphorylase)

ribose-1-arsenate + dihydrolipoate + H+ <=> D-ribofuranose + arsenite + (R)-lipoate

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the direction in which it was curated.

The reaction is favored in the direction shown.

In Pathways: arsenate detoxification I (glutaredoxin)

Summary:
Radabaugh et al have demonstrated that arsenate reductase, isolated from human liver, was identical to PNP [Radabaugh02]. In the presence of lipoate, the ribose-1-arsenate is broken down to ribose and arsenite, completing the reduction. It is still not completely clear whether the DHLP-assisted hydrolysis of ribose-1-arsenate occurs prior to release from the catalytic site . of arsenate to arsenite.

Cofactors or Prosthetic Groups: dihydrolipoate [Radabaugh02]


Enzymatic reaction of: purine ribonucleoside:arsenate alpha-D-ribosyltransferase (purine nucleoside phosphorylase)

a purine ribonucleoside + arsenate <=> a purine base + ribose-1-arsenate

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the Enzyme Commission system.

The reaction is favored in the direction shown.

In Pathways: arsenate detoxification I (glutaredoxin)

Kinetic Parameters:

Substrate
Km (μM)
Citations
ribose-1-arsenate
810.0
[Zannis78]

Exons/Introns:

History:
10/31/2011 (caspi) Merged genes G-8141/NP into HS02151/PNP


References

Bzowska00: Bzowska A, Kulikowska E, Shugar D (2000). "Purine nucleoside phosphorylases: properties, functions, and clinical aspects." Pharmacol Ther 88(3);349-425. PMID: 11337031

Ealick90: Ealick SE, Rule SA, Carter DC, Greenhough TJ, Babu YS, Cook WJ, Habash J, Helliwell JR, Stoeckler JD, Parks RE (1990). "Three-dimensional structure of human erythrocytic purine nucleoside phosphorylase at 3.2 A resolution." J Biol Chem 265(3);1812-20. PMID: 2104852

Kulikowska04: Kulikowska E, Kierdaszuk B, Shugar D (2004). "Xanthine, xanthosine and its nucleotides: solution structures of neutral and ionic forms, and relevance to substrate properties in various enzyme systems and metabolic pathways." Acta Biochim Pol 51(2);493-531. PMID: 15218545

Lewis79: Lewis AS, Lowy BA (1979). "Human erythrocyte purine nucleoside phosphorylase: molecular weight and physical properties. A Theorell-Chance catalytic mechanism." J Biol Chem 254(19);9927-32. PMID: 114517

Pugmire02: Pugmire MJ, Ealick SE (2002). "Structural analyses reveal two distinct families of nucleoside phosphorylases." Biochem J 361(Pt 1);1-25. PMID: 11743878

Radabaugh00: Radabaugh TR, Aposhian HV (2000). "Enzymatic reduction of arsenic compounds in mammalian systems: reduction of arsenate to arsenite by human liver arsenate reductase." Chem Res Toxicol 13(1);26-30. PMID: 10649963

Radabaugh02: Radabaugh TR, Sampayo-Reyes A, Zakharyan RA, Aposhian HV (2002). "Arsenate reductase II. Purine nucleoside phosphorylase in the presence of dihydrolipoic acid is a route for reduction of arsenate to arsenite in mammalian systems." Chem Res Toxicol 15(5);692-8. PMID: 12018991

Silva03: Silva RG, Carvalho LP, Oliveira JS, Pinto CA, Mendes MA, Palma MS, Basso LA, Santos DS (2003). "Cloning, overexpression, and purification of functional human purine nucleoside phosphorylase." Protein Expr Purif 27(1);158-64. PMID: 12509998

Stoychev02: Stoychev G, Kierdaszuk B, Shugar D (2002). "Xanthosine and xanthine. Substrate properties with purine nucleoside phosphorylases, and relevance to other enzyme systems." Eur J Biochem 269(16);4048-57. PMID: 12180982

Williams84: Williams SR, Goddard JM, Martin DW (1984). "Human purine nucleoside phosphorylase cDNA sequence and genomic clone characterization." Nucleic Acids Res 12(14);5779-87. PMID: 6087295

Zannis78: Zannis V, Doyle D, Martin DW (1978). "Purification and characterization of human erythrocyte purine nucleoside phosphorylase and its subunits." J Biol Chem 253(2);504-10. PMID: 412851


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 Sat Dec 20, 2014, BIOCYC14A.