Which molecule acts as an inhibitor of carnitine acyltransferase I?

Carnitine acyltransferase I (also known as carnitine palmitoyltransferase I, or CPT I) is an essential enzyme in the metabolism of fatty acids, specifically involved in transporting long-chain fatty acids into the mitochondria for β-oxidation. This enzyme is located on the outer mitochondrial membrane and facilitates the conversion of acyl-CoA into acyl-carnitine, which can then cross into the mitochondria.

Malonyl CoA is a specific product of fatty acid synthesis and serves as a key regulator of lipid metabolism. Its primary function as an inhibitor of carnitine acyltransferase I highlights its role in ensuring that when the body is engaged in fatty acid synthesis (a state promoted by insulin), there is a decrease in the rate of fatty acid oxidation. This makes physiological sense; when there's ample substrate for fatty acid synthesis, there is less need for the oxidation of fatty acids for energy.

The presence of malonyl CoA prevents the entrance of fatty acids into mitochondrial β-oxidation, thus controlling and coordinating energy use and storage. This regulation is crucial during carbohydrate-rich meals, where the body promotes lipid storage rather than lipid catabolism.

Other molecules listed do not directly inhibit car