Purification and Kinetic Properties of 3β-Hydroxysteroid Dehydrogenase from Bovine Adrenocortical Microsomes1

Abstract
3β-Hydroxysteroid dehydrogenase was purified from bovine adrenocortical micro-somes and its properties were studied. The purified dehydrogenase gave a single homogeneous protein band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and showed no steroid Δ5-Δ-4isomerse activity. The molecular weight of the dehydrogenase was estimated to be 41,000 for the monomer and the isoelectric point was determined to be at pH 6.3. The Km values of the dehydrogenase were 6.2 μM for NAD+ 4.9 mM inst for NADP+ 2.0 μM for pregnenolone, and 5.3 μM for 17α-hydroxypregnenolone. The mechanism of inhibition by trilostane of the dehydrogenase was also examined kinetically. The inhibition was found to be competitive, with K1 values of 0.14 μM for 17α-hydroxy-pregnenolone and 0.38 μM for pregnenolone.