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 adenosine into adenine, inosine into hypoxanthine, and guanosine into guanine, in each case creating ribose phosphate.

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. [3]

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. ^ 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]