Bifunctional enzyme involved in steroid-hormone metabolism and cholesterol biosynthesis (PubMed:11165030, PubMed:12574203, PubMed:12732193, PubMed:12829805, PubMed:19772289, PubMed:20659585). Catalyzes the NADP(H)-dependent reduction of estrogens and androgens and regulates the biological potency of these steroids. Converts estrone (E1) to a more potent estrogen, 17beta-estradiol (E2) (PubMed:12574203, PubMed:12732193, PubMed:19772289). Converts dihydrotestosterone (DHT) to its inactive form 5a-androstane-3b,17b-diol (PubMed:12574203, PubMed:12732193, PubMed:19772289). Converts moderately progesterone to 3beta-hydroxypregn-4-ene-20-one, leading to its inactivation (PubMed:12574203, PubMed:12732193). Additionally, participates in the post-squalene cholesterol biosynthesis, as a 3-ketosteroid reductase (PubMed:11165030, PubMed:12829805, PubMed:20659585). ; [Isoform 3]: Does not have enzymatic activities toward E1 and DHT.
