Cytosolic aldo-keto reductase that catalyzes the NADH and NADPH-dependent reduction of ketosteroids to hydroxysteroids (PubMed:19218247). Most probably acts as a reductase in vivo since the oxidase activity measured in vitro is inhibited by physiological concentrations of NADPH (PubMed:14672942). Displays a broad positional specificity acting on positions 3, 17 and 20 of steroids and regulates the metabolism of hormones like estrogens and androgens (PubMed:10998348). Works in concert with the 5-alpha/5-beta-steroid reductases to convert steroid hormones into the 3-alpha/5-alpha and 3-alpha/5-beta-tetrahydrosteroids. Catalyzes the inactivation of the most potent androgen 5-alpha-dihydrotestosterone (5-alpha-DHT) to 5-alpha-androstane-3-alpha,17-beta-diol (3-alpha-diol) (PubMed:15929998, PubMed:17034817, PubMed:17442338, PubMed:8573067). Also specifically able to produce 17beta-hydroxy-5alpha-androstan-3-one/5alphaDHT (PubMed:10998348). May also reduce conjugated steroids such as 5alpha-dihydrotestosterone sulfate (PubMed:19218247). Displays affinity for bile acids (PubMed:8486699). a 3alpha-hydroxysteroid + NADP(+) = a 3-oxosteroid + H(+) + NADPH a 3alpha-hydroxysteroid + NAD(+) = a 3-oxosteroid + H(+) + NADH 5alpha-androstane-3alpha,17beta-diol + NADP(+) = 17beta-hydroxy-5alpha-androstan-3-one + H(+) + NADPH 5alpha-androstane-3alpha,17beta-diol + NAD(+) = 17beta-hydroxy-5alpha-androstan-3-one + H(+) + NADH 5alpha-androstane-3alpha,17beta-diol + NAD(+) = 3alpha-hydroxy-5alpha-androstan-17-one + H(+) + NADH 17beta-estradiol + NADP(+) = estrone + H(+) + NADPH 17beta-estradiol + NAD(+) = estrone + H(+) + NADH (20S)-hydroxypregn-4-en-3-one + NADP(+) = H(+) + NADPH + progesterone (20S)-hydroxypregn-4-en-3-one + NAD(+) = H(+) + NADH + progesterone 3alpha-hydroxy-5alpha-androstan-17-one + NADP(+) = 5alpha-androstan-3,17-dione + H(+) + NADPH (3beta,5alpha,17beta)-3-hydroxy-androstan-17-yl sulfate + NADP(+) = 5alpha-dihydrotestosterone sulfate + H(+) + NADPH (1R,2R)-1,2-dihydrobenzene-1,2-diol + NADP(+) = catechol + H(+) + NADPH (S)-indan-1-ol + NAD(+) = H(+) + indan-1-one + NADH (S)-indan-1-ol + NADP(+) = H(+) + indan-1-one + NADPH Inhibited by hexestrol with an IC(50) of 2.8 uM, 1,10-phenanthroline with an IC(50) of 2100 uM, 1,7-phenanthroline with an IC(50) of 1500 uM, flufenamic acid with an IC(50) of 0.9 uM, indomethacin with an IC(50) of 75 uM, ibuprofen with an IC(50) of 6.9 uM, lithocholic acid with an IC(50) of 0.07 uM, ursodeoxycholic acid with an IC(50) of 0.08 uM and chenodeoxycholic acid with an IC(50) of 0.13 uM (PubMed:8573067). The oxidation reaction is inhibited by low micromolar concentrations of NADPH (PubMed:14672942). kcat is 0.66 min-1 for the reduction of 17beta-hydroxy-5alpha-androstan-3-one (PubMed:10998348). kcat is 1.98 min-1 for the reduction of 17beta-hydroxy-5alpha-androstan-3-one (PubMed:19218247). kcat is 1.39 min-1 for the reduction of 5alpha-androstan-3,17-dione (PubMed:10998348). kcat is 0.42 min-1 for the oxidation of 3alpha-hydroxy-5alpha-androstan-17-one/androsterone (PubMed:10998348). kcat is 0.24 min-1 for the oxidation of 5alpha-androstane-3alpha,17beta-diol (PubMed:10998348). kcat is 1.0 min-1 for the reduction of 5alpha-dihydrotestosterone sulfate (PubMed:19218247). Steroid metabolism. Expressed in fetal testes. Expressed in fetal and adult adrenal glands. The disease is caused by variants affecting the gene represented in this entry. Belongs to the aldo/keto reductase family.