Steroids as substrates for cholesterol: oxygen oxidoreductase, with special reference to 3beta-hydroxy bile acids.

Cholesterol: oxygen oxidoreductase [EC 1.1.3.6] from Brevibacterium sterolicum (ATCC 21387) was found to catalyze the oxidation of steroids such as sterols, steroid hormones, and bile acids having a free C-3beta hydroxyl group. However, the enzyme was inactive towards estradiol and estriol and had a weak activity towards steroids with functional groups adjacent to the 3beta-hydroxyl group on the steroid nucleus. Variation in the length of the side chain of 3beta-hydroxy steroids had no marked effect on the activity. 3beta-Hydroxy bile acids with delta4 or delta5 were oxidized to almost the same extent as cholesterol. In contrast, 3beta-hydroxy bile acids without delta4 or delta5 were oxidized only to the extent of 1.4--2.1%. 3 beta-Hydroxychol-4 or 5-enoic acid was oxidized in the same way as cholesterol. This enzyme is useful as a simple tool for identification of 3 beta-hydroxy groups of bile acids.