Substrate specificity of mouse 17α-HSD activity of HEK-293 cells stably transfected with pCMVneo-m17α-HSD. The experiments were performed using HEK-293 cells stably expressing 17α-HSD in culture. 0,1 μM of the indicated [14C]-and [3H]-labeled steroid was added to culture medium for one hour. Testo, conversion of testosterone to 4-dione and vice-versa; E1, conversion of estrone to estradiol and vice-versa; DHEA, conversion of dehydroepiandrosterone to 5-diol; 5α-dione, conversion of androstanedione to androsterone (ADT) and vice-versa; DHT, conversion of dihydrotestosterone to 3α-diol and vice-versa; DHP, conversion of dihydroprogesterone to allopregnanolone and vice-versa; Preg and Prog, conversion of pregnenolone and progesterone to 20α-OHPreg and 20α-OHProg. The error bar indicates mean ± SEM of triplicate assays. Incubation, extraction, separation and quantification were performed as described in Materials and Methods.