Final answer:
The correct substance needed to transform free long-chain fatty acids into acylcarnitines is carnitine, which plays a crucial role in transporting fatty acids through the mitochondrial membranes.
Step-by-step explanation:
The transformation of free long-chain fatty acids into acylcarnitines requires carnitine, not choline, arginine, or glutamine. Carnitine facilitates the transport of fatty acids through the mitochondrial membranes by reacting with activated fatty acids in the presence of the enzyme carnitine acyl transferase-I. This reaction forms a fatty acyl-carnitine complex, which is easily transported through the inner mitochondrial membrane by a transport protein known as carnitine acyl carnitine translocase. On the inner surface of the membrane, carnitine acyl transferase-II hydrolyzes the fatty acyl carnitine to produce fatty acyl-CoA and free carnitine, allowing the fatty acyl-CoA to undergo further oxidation in the mitochondrial matrix.