Catalyzes the elimination of the C-1 and C-2 hydrogen atoms of the A-ring from the polycyclic ring structure of 3-ketosteroids. Is also involved in the formation of 1,4-androstadiene-3,17-dione (ADD) from 4-androstene-3,17-dione (AD) to. 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 Cells show an accumulation of 4-androstene-3,17-dione (AD) in the cholesterol degradation process. Belongs to the FAD-dependent oxidoreductase 2 family. 3-oxosteroid dehydrogenase subfamily.