Intramitochondrial localization of palmityl-CoA dehydrogenase, β-hydroxyacyl-CoA dehydrogenase and enoyl-CoA hydratase in guinea-pig heart

Abstract

1. 1. The extent to which mitochondrial enzymes are released from the inner membrane by sonication of guinea-pig heart mitochondria differs for the different enzymes. In increasing order cytochrome c oxidase, fatty acid synthesis, aspartate aminotransferase, β-hydroxyacyl-CoA dehydrogenase, enoyl-CoA hydratase, palmityl-CoA dehydrogenase, malate dehydrogenase, malonyl-CoA decarboxylase and propionyl-CoA carboxylase are, after sonication of the mitochondria, recovered in the soluble fraction. This suggests a certain variability in the extent of binding of the enzymes to the inner side of the mitochondrial inner membrane. 2. 2. None of the enzymes of fatty acid β-oxidation tested shows an intramitochondrial distribution pattern that parallels that of the fatty acid-synthesizing system. This suggests that different enzyme systems are concerned with mitochondrial fatty acid synthesis and breakdown. 3. 3. Sonication of guinea-pig heart mitochondria releases from the inner membrane a greater fraction of the enoyl-CoA hydratase activity with trans-2-hexadecenyl-CoA as substrate than that with crotonyl-CoA, indicating that two different enzymes are concerned. 4. 4. The activity of enoyl-CoA hydratase, purified from beef liver with trans-2-hexadecenyl-CoA as substrate, is only 0.2% of that with crotonyl-CoA. However, the crude beef-liver homogenate shows an enoyl-CoA hydratase activity with trans-2hexadecenyl-CoA that is about 20% of that with crotonyl-CoA. This supports the hypothesis that the hydration of trans-2-hexadecenyl-CoA is catalyzed by an enoyl-CoA hydratase that is not identical with the one that hydrates crotonyl-CoA.