Involved in the second cycle of side chain dehydrogenation in the beta-oxidation of cholesterol catabolism. It contributes partly to the virulence by increasing the efficiency of beta-oxidation (PubMed:26161441). Catalyzes the dehydrogenation of the five-carbon steroid side chain of 3-oxo-chol-4-en-24-oyl-CoA (3-OCO-CoA) to yield 3-oxochol-4,22-dien-24-oyl-CoA (PubMed:26161441). Can also use 3beta-hydroxy-chol-5-ene-24-oyl-CoA, and shows weak activity with cholyl-CoA and deoxycholyl-CoA (PubMed:25645564). 3-oxochol-4-en-24-oyl-CoA + A = (22E)-3-oxo-chol-4,22-dien-24-oyl-CoA + AH2 3beta-hydroxy-chol-5-ene-24-oyl-CoA + A = 3beta-hydroxy-chol-5,22-dien-24-oyl-CoA + AH2 Binds 2 FAD per dimer. kcat is 5 sec(-1) for 3-OCO-CoA as substrate (at pH 8.5 and 25 degrees Celsius (PubMed:26161441). kcat is 3.7 sec(-1) with 3beta-hydroxy-chol-5-ene-24-oyl-CoA as substrate. kcat is 0.22 sec(-1) with cholyl-CoA as substrate. kcat is 0.44 sec(-1) with deoxycholyl-CoA as substrate (PubMed:25645564). Steroid metabolism; cholesterol degradation. Homodimer. Induced by cholesterol and repressed by KstR. Contains two ACAD domains separated by a short linker. The two domains interact to form a single active site. Belongs to the acyl-CoA dehydrogenase family.