Intact alpha-subunit is required for membrane-binding of human mitochondrial trifunctional beta-oxidation protein, but is not necessary for conferring 3-ketoacyl-CoA thiolase activity to the beta-subunit.

We have studied the activities of alpha and beta subunit enzymes of the beta-oxidation trifunctional protein complex in a patient who does not process the alpha-subunit. Long-chain 3-ketoacyl-CoA thiolase, the beta-subunit enzyme, was transported into the mitochondrial matrix, where it expressed normal levels of activity, but was not translocated to the membrane. Thus, intact alpha-subunit is required for trifunctional protein membrane translocation, but is not necessary for conferring activity of the beta-subunit.