Purine nucleoside phosphorylase

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Not to be confused with polynucleotide phosphorylase.
purine-nucleoside phosphorylase
purine-nucleoside phosphorylase. PDB 1rct.[1]
EC number
CAS number 9030-21-1
IntEnz IntEnz view
ExPASy NiceZyme view
MetaCyc metabolic pathway
PRIAM profile
PDB structures RCSB PDB PDBe PDBsum
Gene Ontology AmiGO / EGO
Purine nucleoside phosphorylase
Protein NP PDB 1m73.png
PDB rendering based on 1m73.
Available structures
PDB Ortholog search: PDBe, RCSB
Symbols PNP ; NP; PRO1837; PUNP
External IDs OMIM164050 MGI97365 HomoloGene227 ChEMBL: 4338 GeneCards: PNP Gene
EC number
RNA expression pattern
PBB GE NP 201695 s at tn.png
More reference expression data
Species Human Mouse
Entrez 4860 18950
Ensembl ENSG00000198805 ENSMUSG00000021871
UniProt P00491 P23492
RefSeq (mRNA) NM_000270 NM_013632
RefSeq (protein) NP_000261 NP_038660
Location (UCSC) Chr 14:
20.47 – 20.48 Mb
Chr 14:
50.94 – 50.97 Mb
PubMed search [1] [2]

Purine nucleoside phosphorylase also known as PNPase and inosine phosphorylase is an enzyme that in humans is encoded by the NP gene.[2]


Purine nucleoside phosphorylase is an enzyme involved in purine metabolism. PNP metabolizes inosine into hypoxanthine and guanosine into guanine, in each case creating ribose phosphate. Note: adenosine is first metabolized to inosine via the enzyme adenosine deaminase.[3]

Nucleoside phosphorylase is an enzyme which cleaves a nucleoside by phosphorylating the ribose to produce a nucleobase and ribose 1 phosphate. It is one enzyme of the nucleotide salvage pathways. These pathways allow the cell to produce nucleotide monophosphates when the de novo synthesis pathway has been interrupted or is non-existent (as is the case in the brain). Often the de novo pathway is interrupted as a result of chemotherapy drugs such as methotrexate or aminopterin.

All salvage pathway enzymes require a high energy phosphate donor such as ATP or PRPP.

Adenosine uses the enzyme adenosine kinase, which is a very important enzyme in the cell. Attempts are being made to develop an inhibitor for the enzyme for use in cancer chemotherapy.

Enzyme regulation[edit]

This protein may use the morpheein model of allosteric regulation.[4]

Clinical significance[edit]

PNPase, together with adenosine deaminase (ADA), serves a key role in purine catabolism, referred to as the salvage pathway. Mutations in ADA lead to an accumulation of (d)ATP, which inhibits ribonucleotide reductase, leading to a deficiency in (d)CTPs and (d)TTPs, which, in turn, induces apoptosis in T-lymphocytes and B-lymphocytes, leading to severe combined immunodeficiency (SCID).[citation needed]

PNP-deficient patients will have an immunodeficiency problem. It affects only T-cells; B-cells are unaffected by the deficiency.

See also[edit]


  1. ^ Canduri, F.; Dos Santos, D. M.; Silva, R. G.; Mendes, M. A.; Basso, L. A.; Palma, M. S.; De Azevedo, W. F.; Santos, D. S. (2004). "Structures of human purine nucleoside phosphorylase complexed with inosine and ddI". Biochemical and Biophysical Research Communications 313 (4): 907–914. doi:10.1016/j.bbrc.2003.11.179. PMID 14706628. 
  2. ^ "Entrez Gene: NP nucleoside phosphorylase". 
  3. ^ Kaplan USMLE Biochemistry Review
  4. ^ Selwood T, Jaffe EK (Mar 2012). "Dynamic dissociating homo-oligomers and the control of protein function". Archives of Biochemistry and Biophysics 519 (2): 131–43. doi:10.1016/j.abb.2011.11.020. PMC 3298769. PMID 22182754. 

Further reading[edit]

External links[edit]