Thus, the two substrates of this enzyme are a purine nucleoside and phosphate, whereas its products are a purine and alpha-D-ribose 1-phosphate.
This enzyme belongs to the family of glycosyltransferases, specifically the pentosyltransferases. The systematic name of this enzyme class is purine-nucleoside:phosphate ribosyltransferase.
One of the reaction catalyzed by purine nucleoside phosphorylase in purine metabolism
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.
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.
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