Carnitine palmitoyltransferase I (CPT I) is an enzyme located in the outer mitochondrial membrane. It plays a crucial role in the metabolism of fatty acids by facilitating the transport of long-chain fatty acids into the mitochondria, where they can be oxidized for energy. CPT I converts acyl-CoA into acylcarnitine, allowing fatty acids to cross the mitochondrial membrane. Once inside the mitochondria, the acylcarnitine is converted back to acyl-CoA by another enzyme, carnitine palmitoyltransferase II (CPT II). This process is essential for energy production, especially during periods of fasting or intense exercise when the body relies on fat as a primary energy source.