Joseph M. Margolis

Quantitation of pathways of ethanol metabolism

A method has been developed for estimating the sum of the contributions to ethanol oxidation by the microsomal ethanol-oxidizing system (MEOS) and catalase in the intact liver cell. It depends upon a comparison of the fate of the R hydrogen of ethanol and the hydrogen bound to carbon-2 of sorbitol under identical conditions. Limitations of the approach, particularly as regards isotopic effects, are defined. Under the condition of incubation of liver slices from rat and monkey at a concentration of ethanol of 3 mg/ml and from rat at 1 mg/ml, alcohol dehydrogenase catalysis is concluded to account, on the average, for 89% or more of the initial metabolism of ethanol. As by-products of this study, the stereospecificity of the sorbitol dehydrogenase-catalyzed reaction is shown to be of the A type in the rat, and evidence is obtained for the irreversibility of sorbitol oxidation in the intact liver cell.

Subcellular site of acetaldehyde oxidation in rat liver

Abstract Slices of rat liver were incubated with ( R )ethanol-1- 3 H and ( S )ethanol-1- 3 H at a concentration of 1mg ml . During the course of the incubation, the ethanol in the flask containing the ( S ) isomer. but not the ( R ) isomer, was enriched with 3 H. For the same quantity of 3 H metabolized from the ( R )ethanol-1- 3 H as from the ( S )ethanol-1- 3 H. much less 3 H from the ( S ) than from the ( R ) isomer was incorporated into the lactate formed during the incubation. This indicates that the ( R ) hydrogen has a much greater access than the ( S ) hydrogen to the pool of NADH in the cytosol utilized in the reduction of pyruvate to lactate. It is concluded that the formation of NADH from acetaldehyde occurs under these conditions, primarily in a compartment other than the cytosol. It is presumed that this compartment is mitochondrial.

On the lack of formation of L-(+)-3-hydroxybutyrate by liver.

Abstract The terminal carbon of palmitic acid, traced with 14C, is preferentially incorporated into carbon 4 of hydroxybutyrate formed by hepatocytes and perfused livers from 18- to 19-day-old rats and perfused livers from fasted adult rats. However, 14C from [13-14C]palmitic acid is incorporated into carbon 1 of the hydroxybutyrate to the same extent as any one of the first 12 carbons of palmitic acid as assessed with [1-14C]palmitic acid and [6-14C]palmitic acid. Therefore, the hydroxybutyrate is formed via hydroxymethylglutaryl-CoA, i.e., it is in the d configuration, and hydrolysis of l -hydroxybutyryl-CoA, the intermediate in the β oxidation of the palmitate, does not occur. Further, a negligible amount of 14C remains in hydroxybutyrate formed from 14C-labeled palmitic acid by isolated hepatocytes and perfused livers from the young rats, when the hydroxybutyrate is treated with d -(−)-3-hydroxybutyrate dehydrogenase to convert the d isomer to acetoacetate. Thus, l -(+)-3-hydroxybutyrate is not produced by rat liver as assessed using these preparations.

ω-Oxidation of fatty acids and the acetylation of p-aminobenzoic acid

Abstract p-Aminobenzoic acid was fed to normal and alloxan-induced diabetic rats injected with [ω-14C]labeled and [2-14C]labeled fatty acids. The p-acetamidobenzoic acid that was excreted was hydrolyzed to yield acetate which was degraded. The distribution of 14C in the acetates formed when an [ω-14C]-labeled fatty acid was injected was similar to that when a [2-14C]labeled fatty acid was injected. This contrasts with the finding that in acetates from 2-acetamido-4-phenylbutyric acid excreted when 2-amino-4-phenylbutyric acid was fed, there was a difference in the distributions of 14C, a difference attributable to ω-oxidation of the fatty acid. Acetylation of p-aminobenzoic acid is then concluded to occur in a different cellular environment than that of 2-amino-4-phenylbutyric acid, one in which ω-oxidation is not functional. When 2-amino-4-phenylbutyric acid was fed and [6-14C] palmitic acid injected, rather than [16-14C]palmitic acid, the distribution of 14C in acetate was the same as when [2-14C]palmitic acid was injected. This indicates that the dicarboxylic acid formed on ω-oxidation of palmitic acid does not undergo β-oxidation to form succinyl-CoA. Thus, glucose is not formed via ω-oxidation of long-chain fatty acid.