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Purine nucleoside phosphorylase also known as PNPase and inosine phosphorylase is an enzyme that in humans is encoded by the ''NP'' gene.〔(【引用サイトリンク】 url = http://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=4860 )〕 == Function == 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.〔Kaplan USMLE Biochemistry Review〕 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. * Thymidine can be phosphorylated by thymidine kinase (TK). * Uridine can be phosphorylated by uridine kinase (UK). * Cytidine can be phosphorylated by cytidine kinase (CK). * Deoxycytidine can be phosphorylated by deoxycytidine kinase (DCK). 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Purine nucleoside phosphorylase」の詳細全文を読む スポンサード リンク
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