Transfer of the 1-pro-R and the 1-pro-S hydrogen atoms of ethanol in metabolic reductions in vivo

Abstract

The transfer of deuterium from [1 R-2H]ethanol and [1 S-2H]-ethanol to reduced metabolites of administered compounds was measured in female rats provided with bile fistulas. Administered cyclohexanone was reduced to cyclohexanol, and in this reduction hydrogen was transferred only from the 1-pro-R position of the ethanol. The deuterium content in the cyclohexanol was about 67% of that in the ethanol. In the reduction of the 17-oxo group in 3beta-hydroxy-5alpha-androstan-17-one, hydrogen was transferred both from the 1-pro-R position and the 1-pro-S position, resulting in degrees of labelling that were about 25% and 2%, respectively, of those in the specific positions of the ethanols. The 1-pro-R and 1-pro-S positions of ethanol contributed about 9% and 5%, respectively, of the 3beta hydrogen in lithocholic acid formed from 3-oxo-5beta-cholanoic acid. The results indicate that alcohol dehydrogenase and aldehyde dehydrogenase do not share a common pool of NAD, and that NADH formed during acetaldehyde oxidation is utilized for reductions in the cytosol to a smaller extent than the NADH formed in the alcohol dehydrogenase reaction. This result supports the concept that aldehyde oxidation is mainly an intramitochondrial process. The relatively extensive utilization of the 1-pro-S hydrogen of ethanol in the reduction of 3-oxo-5beta-cholanoic acid, that is probably NADPH-dependent, indicates that cytosolic NADPH may be produced from malate or isocitrate formed intramitochondrially.