The Collaborative International Dictionary of English v.0.48:

inosine \in"o*sine\ ([i^]n"[-o]*s[i^]n), n. (Chem.)
   A ribonucleoside (C10H12N4O5) found in meat and meat
   extracts, differing from adenosine in having a hydroxyl
   rather than an amine attached to the purine ring. It may be
   prepared from adenosine by the enzyme adenosine deaminase, or
   by chemical deamination, as with nitrous acid. It
   participates in some cellular functions, but is not one of
   the normal nucleoside components of RNA.
   [PJC]