purine-nucleoside phosphorylase activity

Definition

Target type: molecularfunction

Catalysis of the reaction: purine nucleoside + phosphate = purine + alpha-D-ribose 1-phosphate. [EC:2.4.2.1]

Purine-nucleoside phosphorylase (PNP) activity is a critical enzymatic process involved in the catabolism of purine nucleosides, such as guanosine and inosine. This activity is catalyzed by the enzyme purine nucleoside phosphorylase (PNP), which plays a vital role in the salvage pathway for purine bases and the regulation of purine nucleotide levels. The molecular function of PNP involves the following steps:

1. **Substrate Binding:** PNP binds to a purine nucleoside, such as guanosine or inosine. The nucleoside is positioned in the active site of the enzyme, where it interacts with specific amino acid residues.

2. **Phosphorolysis:** PNP catalyzes the phosphorolytic cleavage of the glycosidic bond between the purine base and the sugar moiety (ribose or deoxyribose) of the nucleoside. This reaction requires the presence of inorganic phosphate (Pi). The reaction proceeds through a two-step mechanism involving the formation of a covalent intermediate between the enzyme and the purine base.

3. **Product Release:** The reaction releases the purine base (e.g., guanine or hypoxanthine) and the sugar-1-phosphate (e.g., ribose-1-phosphate or deoxyribose-1-phosphate).

4. **Phosphate Utilization:** The inorganic phosphate that was used in the phosphorolysis reaction is regenerated.

The purine base is further metabolized by other enzymes, while the sugar-1-phosphate can be recycled for nucleotide biosynthesis. The molecular function of PNP is essential for maintaining the proper levels of purine nucleotides in cells. Mutations in the PNP gene can lead to a deficiency in PNP activity, which can result in various metabolic disorders, including immunodeficiency and neurodevelopmental issues.'
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Proteins (2)

Compounds (29)