| Abstract: | Under nitrogen atmosphere, methanol oxidase isolated from Candida boidinii catalyzes no hydrogen exchange of ethanol. Reactions with (1R)1-3H]ethanol or (1S)1-3H]ethanol occur stereoselectively. The ratio of hydrogen abstraction in the oxidation of ethanol is about 7:1 in favor of the pro R hydrogen atom. The isotope effect kH/k3H is 2 - 2.5 for (1R)1-3H]ethanol. The isotope effects on Km and V have been determined for four different deuterium-labelled ethanols. The Km for 2H3]methanol is nearly twice that for CH3OH. That is about the same ratio as for ethanol/methanol. For the oxidation of CH3OH and 2H3COH, the ratio of VH/V2H3 = 2.44, while the ratio for methanol/ethanol is only 1.3. It has been conformed that catalase from bovine liver eliminates only the pro R hydrogen atom from ethanol. The isotope effect for the catalase-catalyzed oxidation of (1R)1-3H]ethanol is 2.1. |
