Involved in the degradation of cholesterol (PubMed:18031290, PubMed:21987574). Catalyzes the elimination of the C-1 and C-2 hydrogen atoms of the A-ring from the polycyclic ring structure of 3-ketosteroids (PubMed:18031290). Has a clear preference for 3-ketosteroids with a saturated A-ring, displaying highest activity on 5alpha-AD (5alpha-androstane-3,17-dione) and 5alpha-T (5alpha-testosterone, also known as 17beta-hydroxy-5alpha-androstane-3-one) (PubMed:18031290). Is also involved in the formation of 3-keto-1,4-diene-steroid from 3-keto-4-ene-steroid (PubMed:21987574). Catalyzes the conversion of 3-oxo-23,24-bisnorchol-4-en-22-oyl-coenzyme A thioester (4-BNC-CoA) to 3-oxo-23,24-bisnorchola-1,4-dien-22-oyl-coenzyme A thioester (1,4-BNC-CoA) (PubMed:21987574). A + a 3-oxosteroid = a 3-oxo-Delta(1)-steroid + AH2 A + a 3-oxo-Delta(4)-steroid = a 3-oxo-Delta(1,4)-steroid + AH2 3-oxochol-4-en-22-oyl-CoA + NAD(+) = 3-oxochola-1,4-dien-22-oyl-CoA + H(+) + NADH Deletion mutant is unable to use cholesterol as a source of carbon and energy, and has a limited ability to multiply in resting human macrophages following infection, reflecting a failure of the mutant to inhibit the TLR2-dependent bactericidal activity of resting macrophages. Belongs to the FAD-dependent oxidoreductase 2 family. 3-oxosteroid dehydrogenase subfamily.