Chymotrypsin activates cardiac mitochondrial carnitine-acylcarnitine translocase

The carnitine-acylcarnitine translocase facilitates carnitine and acylcarnitine transport into the mitochondrial matrix during beta-oxidation. Our results demonstrate that chymotrypsin can activate the maximal velocity of N-ethylmaleimide (NEM)-sensitive carnitine or palmitoylcarnitine exchange 7-fold, while doubling the affinity of the translocase for carnitine. Chymotrypsin activation is strictly dependent on the presence of free or short-chain acylcarnitine in the proteolysis medium, the extent of activation decreasing as the acylcarnitine chain length in the proteolysis medium increases. Chymotrypsin treatment decreases the apparent I50 value (inhibitor concentration required to give half-maximal inhibition) of the translocase for inhibition by NEM only under conditions which produce translocase activation. Modification of submitochondrial particle membranes by chymotrypsin does not result in gross ultrastructural changes or in an increase in the passive permeability of these membranes to carnitine. The data suggest that carnitine binding produces a change in translocase conformation which allows chymotrypsin modification to occur. This modification alters the kinetic and inhibitor-binding properties of the translocase.