Rat liver metabolism of dicarboxylic acids

Abstract

Recently, we demonstrated in rat liver that dicarboxylic acids containing more than five carbons can be activated by a microsomal dicarboxylyl-CoA synthetase (J. Vamecq, E. de Hoffmann, and F. Van Hoof. Biochem. J. 230: 683-693, 1985). The products of this reaction, dicarboxylyl-CoA esters, were found to be substrates for an H2O2-generating dicarboxylyl-CoA oxidase. In the present work we report that 1) the catalytic center or the essential domains of dicarboxylyl-CoA synthetase are located at the cytosolic aspect of the endoplasmic reticulum membrane; 2) dicarboxylyl-CoA oxidase is optimally active on dodecanedioyl-CoA and is a peroxisomal enzyme; 3) cyanide-insensitive dodecanedioyl-CoA oxidation (NADH production) is catalyzed by rat liver homogenates. Cell fractionation studies disclose that, similar to dodecanedioyl-CoA oxidase (H2O2 production), the cyanide-insensitive dodecanedioyl-CoA oxidizing activity also belongs to peroxisomes; 4) a dodecanedioyl-CoA oxidoreductase reaction can be assayed by the dichlorphenolindophenol procedure in rat liver homogenates, and the activity is abundant in peroxisomal, mitochondrial, and soluble fractions; 5) by contrast with monocarboxylyl-CoA esters, the dicarboxylyl-CoAs are apparently not substrates for mitochondrial fatty acid oxidation; however, the use of dicarboxylylcarnitine esters as direct substrate for mitochondria suggests the existence of an active beta-oxidation of dicarboxylates in these organelles, which is further confirmed by experiments in which mitochondria are permeabilized with digitonin; 6) the in vivo oxidation of infused dodecanedioic acid results in a rapid appearance in urine of medium-chain dicarboxylic acids, with only 30-50% of the infused dose recovered in urine.