1.1.3.28 inosine + O2 = 9-riburonosylhypoxanthine + H2O Other purine and pyrimidine nucleosides, as well as 2'-deoxynucleoside, are substrates, but ribose and nucleotides are not substrates. The overall reaction takes place in two separate steps: 1. 2 inosine + O2 = 2 5'-dehydroinosine + 2 H2O. 2. 2 5'-dehydroinosine + O2 = 2 9-riburonosylhypoxanthine + 2 H2O, with the 5'-dehydro nucleoside being released from the enzyme to serve as substrate for the second reaction. This enzyme differs from EC 1.1.3.39, nucleoside oxidase (H2O2-forming), as it produces water rather than hydrogen peroxide -