Two enzymic processes that are localized in the mitochondrial outer membrane, namely fatty acid oxidation and substrate level phosphorylation, have been found to be inhibited by atractyloside. This sensitivity was demonstrated not only in the intact mitochondrion but also in isolated fractions prepared from the outer membrane. Atractyloside inhibition of these two processes was reversed by sulfhydryl agents and by reducing agents but not by adenine nucleotides. One of the enzymic activities responsible for the atractyloside sensitivity of the β-oxidation sequence was found to be the β-ketoacyl-CoA thiolase. This enzymic activity was as sensitive to atractyloside as was the overall oxidation of fatty acids; the inhibition was reversed by mercaptoethanol. Two of the enzymes involved in substrate level phosphorylation, succinyl thiokinase and nucleoside diphosphokinase, were found to be atractyloside-sensitive. Succinyl thiokinase was identified with the atractyloside-sensitive site of substrate-level phosphorylation because it was as sensitive to the inhibitor as was the overall process; nucleoside diphosphokinase was considerably less sensitive to atractyloside. Individual enzymes in the outer membrane that participate in fatty acid oxidation and substrate-level phosphorylation accounted fully for the atractyloside sensitivity of these processes.
ASJC Scopus subject areas
- Molecular Biology