3-beta-HSD is a bifunctional enzyme, that catalyzes the oxidative conversion of Delta(5)-ene-3-beta-hydroxy steroid, and the oxidative conversion of ketosteroids. The 3-beta-HSD enzymatic system plays a crucial role in the biosynthesis of all classes of hormonal steroids. May be involved in local production of progesterone. a 3beta-hydroxy-Delta(5)-steroid + NAD(+) = a 3-oxo-Delta(5)-steroid + H(+) + NADH a 3-oxo-Delta(5)-steroid = a 3-oxo-Delta(4)-steroid Lipid metabolism; steroid biosynthesis. Expressed in skin and testis. Earliest isoform to be expressed during embryogenesis in cells of embryonic origin at 7 and 9.5 dpc, and is the major isoform expressed in uterine tissue at the time of implantation (4.5 dpc) and continues to be expressed in uterine tissue at 6.5, 7.5 and 9.5 dpc. It is expressed in giant trophoblasts at 9.5 dpc and is expressed in the placenta through 15.5 dpc. Belongs to the 3-beta-HSD family.