Biochemistry II

The first step in utilizing the fatty acid molecule for energy production is the conversion of the fatty acid to a CoA molecule in a two‐step process:

Note that the hydrolysis of two high‐energy phosphate bonds in ATP provides the energy source for the reaction. The inorganic pyrophosphate, PP _i, is subsequently broken down to two phosphate ions by inorganic pyrophosphatase. The action of this enzyme means that very little PP _i remains in the cell, making the synthesis of the fatty acyl‐CoA favored. This is an example of metabolic coupling, the process whereby a thermodynamically unfavored reaction is allowed because it shares an intermediate (in this case PP _i) with a favored one.