inosin

Inosin, or inosine in English, is a purine nucleoside consisting of the nucleobase hypoxanthine bound to a ribose sugar through a β-N9-glycosidic bond. It is a natural component of RNA, most prominently occurring at the wobble position of certain transfer RNAs (tRNAs). Inosine is typically produced in RNA by the deamination of adenosine at the wobble position, a reaction carried out by adenosine deaminases.

In metabolism and RNA biology, inosine has several key roles. In tRNA, the presence of inosine at the anticodon loop broadens codon recognition, because inosine can pair with multiple nucleobases (adenine, cytosine, and uracil) during translation. Inosine can also arise during RNA editing and turnover. In purine metabolism, inosine can be generated or interconverted through pathways that involve dephosphorylation or deamination, and the salvage of hypoxanthine to IMP via hypoxanthine-guanine phosphoribosyltransferase (HGPRT) links inosine-related catabolic products to nucleotide synthesis.

Beyond its natural biological roles, inosine has been used in research and medicine. Inosine pranobex (also known as isoprinosine) is a pharmaceutical compound that combines inosine with other agents and is employed in some countries as an immunomodulatory or antiviral therapy. In laboratory settings, inosine serves as a substrate in nucleotide metabolism studies and as a tool for probing RNA structure and base-pairing properties.

Overall, inosine is a biologically significant nucleoside with established roles in RNA biology and purine metabolism, as well as limited clinical applications through related compounds.