Beta oxidation is the major pathway for catabolism of fatty acids in mitochondria of cell, in which two carbons are successively removed from the carboxyl end of fatty acyl CoA producing acetyl CoA, NADH, and FADH2. The fatty acid is broken between alpha(2) and beta(2) carbon atoms – hence the name beta oxidation. It is an aerobic process requiring oxygen. Fatty acid oxidation generates large quentities of ATP.
Steps of beta oxidation of fatty acids:
At first, fatty acid must be converted into an active intermediate (aceyl CoA) in the cytoplasm of cell before they can be catabolized. In the presence of ATP, aceyl CoA synthetase enzyme catalyzes the conversion of fatty acid into aceyl CoA (active fatty acid). Active short chain and medium chain fatty acids (containing less than 12 carbon atoms) can enter from cytoplasm into mitochondria without difficulty, but long chain fatty acid must be bound to carnitine to penetrate the inner mitochondrial membrane and gain access to mitochondria for beta oxidation.
The first cycle of beta oxidation consists of a sequence of four reactions, which result in shortening the fatty acid chain by two carbons (for saturated fatty acid with even number of carbon atoms) or three carbons residue (for saturated fatty acid with an odd number of carbon atoms). The reactions include an oxidation that yields FADH2, a hydration reaction, a second oxidation reaction that yields NADH, and a thiolytic reaction that produces a molecule of acetyl CoA. These four reactions occur repeatately. Each cycle of reactions producing one acetyl CoA, one NADH, and one FADH2.
Energy generation from beta oxidation of fatty acids:
Energy generation from beta oxidation of fatty acids depend on the number of carbon atoms present in fatty acid. Fatty acids containing more carbon atoms generate more energy. For example, caproic acid is a 6 carbon atoms fatty acid, catabolism of one mol of caproic acid ultimately generates 44 mol of ATP.
Fatty acid oxidation disorder:
Fatty acid oxidation disorder can be produced by carnitine deficiency or genetic defects in enzymes involved in the transfer of long chain fatty acid into the mitochondria. This disorder causes cardiomyopathy and hypoketonemic hypoglycemia with coma.