3 alpha-hydroxysteroid dehydrogenase in the cytosol of rat submandibular gland

We examined the in vitro shuttle metabolism between dihydrotestosterone (DHT) and 5 alpha-androstane-3 alpha, 17 beta-diol (3 alpha-diol) by 3 alpha-hydroxysteroid dehydrogenase (3 alpha-HSD, E.C. 1.1.1.50) in rat submandibular gland (SMG) and ventral prostate (VP). The protein having molecular weight of 30 kDa, which was revealed by Sephacryl S-200 column chromatography, had 3 alpha-HSD activity to produce 3 alpha-diol from DHT, and also showed an oxidative 3 alpha-HSD (3 alpha-HSDO) ability to produce DHT from 3 alpha-diol. From the kinetic studies, the apparent Km and Vmax values of 3 alpha-HSD for DHT and NADPH were 6.4 microM, 1429 pmol/mg protein per min and 33.0 microM, 1205 pmol in SMG, and 9.3 microM, 377 pmol and 34.0 microM, 192 pmol in VP. The corresponding values of 3 alpha-HSDO for 3 alpha-diol and NADP+ were 18.0 microM, 714 pmol and 14.0 microM, 445 pmol in SMG, and 14.0 microM, 417 pmol and 36.0 microM, 77 pmol in VP. The affinities for DHT and 3 alpha-diol and the cosubstrate requirements of this enzyme in SMG were similar to those in VP. However, higher capacities of 3 alpha-HSD and 3 alpha-HSDO in SMG than in VP were shown. This suggests that there may be more 3 alpha-HSD in the SMG.