Dealkylation of 24-ethylsterols by Tetrahymena pyriformis.

When Tetrahymena pyriformis was incubated with sitosterol ([24R]-24-ethylcholest-5-en-3 beta-ol]) or its trans-delta22-derivative (stigmasterol), the C-24-dealkylated product, cholesta-5,7,trans-22-trien-3 beta-ol, was obtained in both cases. 24(S)-24-Ethylcholesta-5,7,trans-22-trien-3 beta-ol also was found to be a metabolite. When sitosterol was the substrate, 24(R)-24-ethylcholesta-5,7-dien-3 beta-ol was obtained as a third product. Identifications were made by mass spectroscopy, quantitative chromatography, labeling with 14C, and by other means. The dealkylated product (cholestratrienol) represented 30 percent of the sterols isolable after incubation. The administration of sterols to this organism did not induce sterol biosynthesis, since 2-14C-mevalonate failed to yield radioactive sterol in the presence of added stigmasterol.