Dealkylation of 24‐ethylsterols byTetrahymena pyriformis

Abstract

WhenTetrahymena pyriformis was incubated with sitosterol ([24R]-24-ethylcholest-5-en-3β-ol]) or itstrans-Δ²²-derivative (stigmasterol), the C-24-dealkylated product, cholesta-5,7,trans-22-trien-3β-ol, was obtained in both cases. 24(S)-24-Ethylcholesta-5,7,trans-22-trien-3β-ol also was found to be a metabolite. When sitosterol was the substrate, 24(R)-24-ethylcholesta-5,7-dien-3β-ol was obtained as a third product. Identifications were made by mass spectroscopy, quantitative chromatography, labeling with¹⁴C, and by other means. The dealkylated product (cholestratrienol) represented 30% 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.