Bifunctional enzyme involved in steroid-hormone metabolism and cholesterol biosynthesis (PubMed:12574203, PubMed:12732193, PubMed:12829805, PubMed:20659585, PubMed:19772289, PubMed:11165030). 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:12829805, PubMed:20659585, PubMed:11165030). Does not have enzymatic activities toward E1 and DHT. 17beta-estradiol + NADP(+) = estrone + H(+) + NADPH a 3beta-hydroxysteroid + NADP(+) = a 3-oxosteroid + H(+) + NADPH 3-dehydro-4alpha-methylzymosterol + H(+) + NADPH = 4alpha-methylzymosterol + NADP(+) H(+) + NADPH + zymosterone = NADP(+) + zymosterol 4alpha-methyl-5alpha-cholest-8-en-3-one + H(+) + NADPH = 4alpha-methyl-5alpha-cholest-8-en-3beta-ol + NADP(+) 4alpha-methyl-5alpha-cholest-7-en-3beta-ol + NADP(+) = 4alpha-methyl-5alpha-cholest-7-en-3-one + H(+) + NADPH 5alpha-cholest-8-en-3-one + H(+) + NADPH = 5alpha-cholest-8-en-3beta-ol + NADP(+) 5alpha-androstane-3beta,17beta-diol + NADP(+) = 17beta-hydroxy-5alpha-androstan-3-one + H(+) + NADPH H(+) + NADPH + progesterone = 3beta-hydroxypregn-4-ene-20-one + NADP(+) Estradiol 17-beta-dehydrogenase and dihydrotestosterone oxidoreductase activities are selectively inhibited by 4-methyl-4-aza-5alpha-androstane derivatives, such as 17beta-[(N-Heptyl)methylamino]-4-aza-5r-androstan-3-one and 17beta-(N-Decylformamido)-4-aza-5r-androstan-3-one. Steroid biosynthesis; estrogen biosynthesis. Steroid biosynthesis; zymosterol biosynthesis; zymosterol from lanosterol: step 5/6. Binds to the short form of prolactin receptor. Highly expressed in adrenal gland, liver, lung and thymus. Expressed in breast, ovaries, pituitary gland, pregnant uterus, prostate, kidney, lymph node, small intestine, spinal cord and trachea. Weakly expressed in all other tissues tested. Expressed in eye ciliary epithelial cells and neuroendocrine cells. Phosphorylated. Belongs to the short-chain dehydrogenases/reductases (SDR) family. ERG27 subfamily.