What does CoA have to do with fatty acid metabolism?
In order to participate in any metabolic process, fatty acids must first be activated. They are activated by being joined in thioester linkage (R-CO-SCoA) to the -SH group of coenzyme A. The thioester bond is a high energy bond. This is apparently because resonance structures which can occur in esters with alcohols, and which stabilizes them, cannot occur in thioesters. The greater size of the sulfur atom (compared to the carboxyl oxygen) diminishes the stability of the resonance forms. If the structure has less resonance stability, the energy released upon their hydrolysis will be greater.
