Stereochemically distinct roles for sterol in Saccharomyces cerevisiae.

Cholesterol, (E)- but not (Z)-17(20)-dehydrocholesterol, 5 alpha-cholestan-3 beta-ol, sitosterol, and certain other sterols lacking a 24 beta-methyl group will replace (spare) most but not all of the 24 beta-methylsterol which has recently been found to be absolutely necessary for growth of oxygen-deprived wild type Saccharomyces cerevisiae in the presence of 2,3-iminosqualene. The results imply the existence of two stereochemically distinct roles for sterol in this organism. One of them (perhaps regulatory) requires, whereas the other (probably playing the so-called "bulk" membranous role) does not require the presence of the 24 beta-methyl group. The latter function, for which most of the sterol is needed, can be performed by various 24-alkyl- and 24-desalkylsterols.