Catalyzes the elimination of the C-1 and C-2 hydrogen atoms of the A-ring from the polycyclic ring structure of 3-ketosteroids. A + a 3-oxosteroid = a 3-oxo-Delta(1)-steroid + AH2 Lipid metabolism; steroid degradation. By steroids. Belongs to the FAD-dependent oxidoreductase 2 family. 3-oxosteroid dehydrogenase subfamily.