ß-Oxidation pathway:

An individual reaction included in the degradation of fatty acids through β- oxidation is as bellows:

1.  Oxidation of the fatty acyl CoA to enoyl CoA forming a trans Δ²-double bond on the fatty acyl chain and producing FADH₂   (catalyzed through acyl CoA dehydrogenase).

2.  Hydration of the trans Δ²-enoyl CoA to form 3-hydroxyacyl CoA (catalyzed through enoyl CoA hydratase).

3.  Oxidation   of 3-hydroxyacyl   CoA   to 3-ketoacyl   CoA   producing   NADH (catalyzed through hydroxyacyl CoA dehydrogenase).

4.  Cleavage,  or thiolysis,  of 3-ketoacyl  CoA through a second CoA molecule,  providing acetyl CoA and an acyl CoA shortened by two carbon atoms (catalyzed through β- ketothiolase).

Thus, the breakdown of individual fatty acids occurs as a repeating sequence of four reactions: oxidation (through FAD), hydration, oxidation (by NAD⁺) and thiolysis. These four reactions form one 'round' of fatty acid degradation and their whole effect is to erased two-carbon units sequentially in the form of acetyl CoA from the fatty acid chain. The cleavage of the Δ² (or β) bond of the fatty acyl chain (top structure, for nomenclature) provides fatty acid breakdown its other name, β-oxidation.  The reduced acyl CoA then undergoes further cycles of β-oxidation until the final cycle when the acyl CoA with four carbon atoms is dividing into two molecules of acetyl CoA. Thus a C16 saturated acyl CoA, like as palmitoyl  CoA, would be completely  degraded  into eight molecules  of acetyl CoA through seven rounds of degradation, leading to the whole equation:

Mitochondria  hold  three  acyl  CoA  dehydrogenases  that  act on medium-  short- and long-chain  acyl CoAs  correspondingly.  In compare,  there is just one each  of  the  enzymes  hydroxyacyl  CoA  dehydrogenase, enoyl  CoA  hydratase  and β-ketothiolase  that all have a wide specificity  with respect to the length of the acyl chain.

Figure:   Summary of the reactions involved in the degradation of fatty acids.

In animals  the acetyl CoA produced from fatty acid degradation cannot be converted into oxaloacetate or pyruvate. Although the two carbon atoms from acetyl CoA enter the citric acid cycle they are both oxidized to CO₂ in the reactions catalyzed through isocitrate dehydrogenase and α-ketoglutarate dehydrogenase.  Thus, animals cannot convert fatty acids into glucose. In compare, plants have two further enzymes, isocitrate lyase  and  malate synthase, which enable them to convert  the  carbon  atoms of acetyl CoA into oxaloacetate. This is accomplished via the glyoxylate pathway, a route including enzymes of both the mitochondrion and the glyoxysome and a specialized membranous plant organelle.