Abstract
Peroxidation of ethanol catalyzed by rat liver catalase exhibits an isotope effect with [(1R)-l−3H1ethanol of 2.52 ± 0.21 at pH 6.3–7.7 and 37°C. This value was not affected by changes in either enzyme, substrate or product concentration. Under similar conditions horse liver alcohol dehydrogenase exhibited an isotope effect of 4.16±0.21 in the initial reaction. In the presence of the reaction products the isotope effect was lower. The isotope effect itself was insensitive to 4-methylpyrazole. In preliminary experiments with rat liver microsomes the catalase peroxidation of ethanol could be recognized on the basis of the isotope effect when H2O2 was generated. However, in the same microsomes ethanol oxidation exhibited a considerably higher isotope effect during generation of NADPH. In perfused rat liver the isotope effect at low concentration of ethanol is in accordance with the view that the oxidation of ethanol to acetaldehyde proceeds almost quantitatively via alcohol dehydrogenase. At higher concentrations of ethanol and especially in the presence of 4-methylpyrazole the isotope effect was higher.
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