Search

The intermediates in the biological breakdown and synthesis of fatty acids are S-acyl derivatives of coenzyme A. Fatty acid synthesis is accomplished through repetition of a cycle of four consecutive reactions: a. Condensation of two molecules of acetyl CoA to form acetoacetyl CoA and coenzyme A (CoASH); b. reduction of acetoacetyl CoA to β-hydroxybutyryl CoA; c. dehydration of β-hydroxybutyryl CoA to crotonyl CoA, and d. reduction of crotonyl CoA to butyryl CoA. A new cycle is started by the reaction of butyryl CoA with another molecule of acetyl CoA to form β-keto-caproyl CoA + CoA-SH, and so forth. The cycle is repeated eight times until stearyl CoA is formed. All four reactions of the fatty acid cycle are reversible and fatty acid oxidation, once the fatty acid is activated through conversion to the corresponding S-acyl CoA derivative, proceeds by a reversal of the above sequence. There are two main mechanisms for activation of fatty acids: (a) By a reaction with ATP and CoA to form S-acyl CoA, adenosine monophosphate and pyrophosphate, and (b) by transfer of CoA from certain acyl CoA compounds such as acetyl CoA or succinyl CoA. The isolation and identification of some of the key enzymes of fatty acid metabolism is outlined and their mechanism of action discussed.