beta-oxidation

Most tissues utilize fatty acids as a major source of energy. Fatty acids are more highly reduced than carbohydrates, providing more energy during oxidation. Mitochondrial beta-oxidation of fatty acyl-CoAs is the first stage of utilization – the fatty acylCoA is reduced in a sequence of steps with released energy captured by the reduced energy carriers NADH and FADH₂. Four enzymatic reactions split the molecule at the single CC bond between the (alpha) and (beta) carbons: dehydrogenation by long chain acyl-CoA dehydrogenase (FAD⁺), hydration, dehydrogenation (NAD⁺), and thiolysis. The cycle is repeated, shortening the fatty acyl-CoA by two Cs, in the "beta oxidation spiral".

Ultimately, even-chained fatty acids yield 2-C acetyl-CoA while odd-chained fatty acids yield 3-C propionyl-CoA. The 2-C acetyl-CoA generated in beta-oxidation enters the Krebs cycle, where it is further oxidized to CO₂, producing more reduced energy carriers (NADH & FADH₂). The 3-C propionyl-CoA is converted to succinyl-CoA, which then enters the Krebs cycle. The reduced energy carriers transfer their energy to the electron transport chain where they drive the proton gradient that supports mitochondrial ATP production.

Beta-oxidation Pathway : Beta-Oxidation of Fatty Acids (even chain) : Beta-oxidation of Fatty Acids (odd chain)