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)


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