Acyl-carnitine is the form of transport a fatty acid takes in traversing the mitochondrial inner membrane. Acyl-CoAs in the cytoplasm are converted to acyl-carnitine derviatives by action of carnitine acyltransferase I on the outer portion of the mitochondrial inner membrane (Figure 18.15).

A translocase carries the acyl-carnitine into the mitochondria. Once inside the mitochondrial matrix, carnitine is replaced on the acyl group by CoASH in a reaction catalyzed by carnitine acyltransferase II.