Fatty acid degradation is the process in which fatty acids are broken down into their metabolites, resulting in release of its energy to the target cells. It includes three major steps:
Initially in the process of degradation, fatty acids are stored in fat cells (adipocytes). The breakdown of this fat is known as lipolysis. The products of lipolysis, free fatty acids, are released into the bloodstream and circulate throughout the body.
The enzyme first catalyzes nucleophilic attack on the α-phosphate of ATP to form pyrophosphate and an acyl chain linked to AMP. The next step is formation of an activated thioester bond between the fatty acyl chain and Coenzyme A.
The formula for the above is:
RCOO- + CoA + ATP + H2O → RCO-CoA + AMP + PPi + 2H+
This two-step reaction is freely reversible and its equilibrium lies near 1. To drive the reaction forward, the reaction is coupled to a strongly exergonic hydrolysis reaction: the enzyme inorganic pyrophosphatase cleaves the pyrophosphate liberated from ATP to two phosphate ions. Thus the net reaction becomes:
RCOO- + CoA + ATP + H2O → RCO-CoA + AMP + 2Pi + 2H+
The inner mitochondrial membrane is impermeable to fatty acids and a specialized carnitine carrier system operates to transport activated fatty acids from cytosol to mitochondria.
It is important to note that carnitine acyltransferase I undergoes allosteric inhibition as a result of malonyl-CoA, an intermediate in fatty acid biosynthesis, in order to prevent futile cycling between beta-oxidation and fatty acid synthesis.
Once inside the mitochondria, the β-oxidation of fatty acids occurs via four recurring steps: