The carbon chain of fatty acids is shortened by 2 carbon atoms at a time. This involves successive reactions catalysed by 4-enzymes. These act the following order:

(A) Acetyl CoA dehydrogenase, β-OH acyl CoA
dehydrogenase, enoyl hydrase, thiolose
(B) Acyl CoA dehydrogenase, thiolase, enoyl
hydrase, β-OH acyl CoA dehydrogenase
(C) Acyl CoA dehydrogenase, thiolose, enoyl
hydrase, β-OH acyl CoA dehydrogenase
(D) Enoyl hydrase, β-OH acyl CoA dehydrogenase,
acyl CoA dehydrogenase, thiolose,