Oxidation of Acetaldehyde by Rat‐Liver Mitochondria in Relation to Ethanol Oxidation and the Transport of Reducing Equivalents across the Mitochondrial Membrane

Abstract

The primary product of the well‐known oxidation of acetaldehyde by rat liver mitochondria is acetate. About 50% of the acetate formed from acetaldehyde is converted to ketone bodies under the experimental conditions used. The oxidation of acetaldehyde by rat liver mitochondria is catalyzed mainly by an aldehyde: NAD oxidoreductase present in the matrix compartment of the mitochondria. About 20% of the total mitochondrial acetaldehyde dehydrogenase activity may be confined to the outer membrane or the intermembrane space. The enzyme has a broad substrate specificity, pH‐optimum at about pH 9.0 and is inhibited by tetraethylthiuram disulfide, chloral hydrate and arsenite. The enzyme is steroid‐insensitive. Two Km‐values for acetaldehyde, below 0.1 μM and 1.0 mM, and two Km‐values for NADM+, 2 μM and 50 μM, were obtained with a partially purified 100000 ×g supernatant. The presence of two aldehyde dehydrogenases in rat liver mitochondria could not be shown. Oxidation of acetaldehyde by rat liver mitochondria causes an inhibition of the production of 14Co2, from [14C]palmitate. The inhibition can be accounted for by dilution of the acetyl‐coenzyme A pool of the mitochondria. The 3‐hydroxybutyrate/acetoacetate ratio during acetaldehyde oxidation is kept at the same level as during oxidation of oleate plus coenzyme A. The mitochondrial acetaldehyde dehydrogenase activity is 80% of the total acetaldehyde dehydrogenase activity of rat liver. The results are discussed with regard to the oxidation of acetaldehyde and to the transfer of reducing equivalents from cytosol to mitochondria during ethanol metabolism. Copyright © 1973, Wiley Blackwell. All rights reserved