Involved in the degradation of cholesterol (PubMed:16000729). Catalyzes the elimination of the C-1 and C-2 hydrogen atoms of the A-ring from the polycyclic ring structure of 3-ketosteroids (By similarity). Is also involved in the formation of 3-keto-1,4-diene-steroid from 3-keto-4-ene-steroid (By similarity). 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 Belongs to the FAD-dependent oxidoreductase 2 family. 3-oxosteroid dehydrogenase subfamily.