Involved in the first cycle of side chain dehydrogenation in the beta-oxidation of cholesterol catabolism (PubMed:26161441). It contributes partly to the virulence by increasing the efficiency of beta-oxidation. Catalyzes the dehydrogenation of acyl-CoA ester side chains of (25S)-3-oxo-cholest-4-en-26-oyl-CoA (3-OCS-CoA) to yield (24E)-3-oxo-cholest-4,24-dien-26-oyl-CoA (PubMed:26348625, PubMed:26161441). Also able to dehydrogenate steroyl-CoA such as 3-oxo-chol-4-en-24-oyl-CoA (3-OCO-CoA) as well as 3-oxo-4-pregnene-20-carboxyl-CoA (3-OPC-CoA) (PubMed:26161441). It dehydrogenates only (25S)-OCS-CoA diastereomer (PubMed:26348625, PubMed:26161441). (25S)-3-oxocholest-4-en-26-oyl-CoA + A = 3-oxo-cholest-4,24-dien-26-oyl-CoA + AH2 Binds 1 FAD per heterodimer. Uncompetitively inhibited by high concentration of 3-OCS-CoA. kcat is 2.7 sec(-1) for 3-OCS-CoA as substrate (at pH 8.5 and 25 degrees Celsius). kcat is 1.5 sec(-1) for 3-OPC-CoA as substrate (at pH 8.5 and 25 degrees Celsius). kcat is 0.48 sec(-1) for 3-OCO-CoA as substrate (at pH 8.5 and 25 degrees Celsius). kcat is 0.042 sec(-1) for octanoyl-CoA as substrate (at pH 8.5 and 25 degrees Celsius). Steroid metabolism; cholesterol degradation. Heterotetramer (dimer of heterodimers) composed of FadE26 and FadE27. Induced by cholesterol and repressed by KstR. Belongs to the acyl-CoA dehydrogenase family.