OXIDATION OF REDUCING EQUIVALENTS DURING ETHANOL METABOLISM. STUDIES WITH 1−3H-ETHANOL

The rate of transfer of reducing equivalents from cytosolic NADH to the mitochondrial cell compartment has been estimated in isolated hepatocytes from fasted rats. Hepatocytes were incubated with 6 mM R-ethanol-1−3 H or 6 mM S-ethanol-1−3H. Measurements of the incorporation of tritium into water and β-hydroxybutyrate allowed calculations of the rate of NAD-dependent shuttles (probably the malate-aspartate shuttle) as well as the rate of FAD-dependent shuttles (probably the α-glycerophosphate shuttle). Incorporation of tritium from R- and Sr-ethanol-1−3H into lactate and glucose showed that less than 20% of the acetaldehyde oxidation takes place in the cytosolic compartment of the liver cell. With an ethanol oxidation rate of 2.5 μmoles × min−1 × ml of cells−1, the activity of the mal ate-aspartate shuttle was estimated to be about 1.5 μmoles × min c ml of cells−1 and that of the α-glycerophosphate shuttle to be about 0.6 μmoles × min−1 × ml of cells−1.