What is one regulatory role of Malonyl-CoA in metabolism?

Malonyl-CoA plays a significant regulatory role in metabolism, particularly in fatty acid metabolism. It is primarily involved in the inhibition of fatty acid catabolism by regulating the transport of fatty acids into the mitochondria. Specifically, malonyl-CoA inhibits carnitine acyltransferase I, the enzyme responsible for transporting long-chain fatty acids into the mitochondria for β-oxidation. This inhibition prevents the breakdown of fatty acids while simultaneously promoting their synthesis, a process known as lipogenesis.

By regulating the balance between synthesis and degradation of fatty acids, malonyl-CoA ensures that the body can manage energy sources effectively, aligning the energy input and output based on metabolic needs. This highlights its decisive role in maintaining metabolic homeostasis.

The other options do not accurately reflect the specific function of malonyl-CoA. For instance, while it may influence aspects of glycolysis, its direct regulatory role is not to activate this pathway. Additionally, malonyl-CoA does not serve to inhibit the TCA cycle or stimulate protein synthesis, which are regulated by different mechanisms and metabolites in the cell.