GO:0047787:   delta4-3-oxosteroid 5beta-reductase activity
Catalysis of the reactions: (1) 5beta-cholestan-3-one + NADP+ = cholest-4-en-3-one + NADPH + H+ and (2) 17,21-dihydroxy-5beta-pregnane-3,11,20-trione + NADP+ = cortisone + NADPH + H+.