Vamecq, Joseph, Vallee, Louis, Fontaine, Monique, Lambert, Didier, Poupaert, Jacques, and Nuyts, Jean-Pierre
In rat liver homogenates fortified with the appropriate cofactors (ATP and CoA), valproic acid induced H2O2production rates by far lower than those recorded on the straight medium‐chain fatty acid n‐octanoic acid. Using directly the CoA esters of these carboxylic acids as substrates for the rat liver H2O2‐generating enzyme activities, valproyl‐CoA, and n‐octanoyl‐CoA were found to induce similar oxidation rates. In the rat liver homogenates, cyanide‐insensitive valproyl‐CoA and octanoyl‐CoA oxidations occurred at rates similar to those of valproyl‐CoA and octanoyl‐CoA oxidase(s), respectively. Studies on fractions obtained from rat liver postnuclear supernatants by isopycnic centrifugation on a linear sucrose density gradient disclose that the density distribution of valproyl‐CoA oxidase superimposes to those of catalase, fatty acyl‐CoA oxidase and cyanide‐insensitive fatty acyl‐CoA oxidation, three peroxisomal marker activities. By contrast, the cyanide‐insensitive valproyl‐CoA oxidation does not adopt the typical peroxisomal distribution of these activities but rather exhibits a mitochondrial localization with, however, a minor peroxisomal component. Interestingly enough, the comparative study of rat tissue distribution, inducibility by clofibrate and sensitivity to deoxycholate indicated that valproyl‐CoA oxidase is an enzyme distinct from fatty acyl‐CoA oxidase and bile acyl‐CoA oxidase. Taken as a whole, the results presented here support the occurrence of a peroxisomal oxidation of the CoA ester of valproic acid and its Δ4‐enoic derivate which might be characterized by two major features: initiation by an acyl‐CoA oxidase distinct from fatty and bile acyl‐CoA oxidases, and inability to complete the β‐oxidation cycle which would not proceed, at significant rates, further than the β‐hydroxyacyl‐CoA dehydrogenation step in peroxisomes.