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Dehydrogenation and dealkylation of various sterols by Tetrahymena pyriformis
Author(s) -
Mallory Frank B.,
Conner Robert L.
Publication year - 1971
Publication title -
lipids
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.601
H-Index - 120
eISSN - 1558-9307
pISSN - 0024-4201
DOI - 10.1007/bf02533028
Subject(s) - tetrahymena pyriformis , squalene , sterol , biosynthesis , chemistry , stereochemistry , biochemistry , cycloartenol , alcohol , lanosterol , tetrahymena , biology , organic chemistry , cholesterol , enzyme
Sterols are not found in Tetrahymena pyriformis when this protozoan is grown in a medium free from exogenous sterols; instead, the principal solid alcohol that can be isolated from the organism is tetrahymanol. a pentacyclic triterpenoid alcohol with an unusual structure. The biosynthesis of tetrahymanol has been shown by appropriate labeling studies to involve a direct, nonoxidative, proton‐initiated cyclization of squalene rather than the more commonly found type of mechanism involving squalene 2,3‐oxide as an intermediate. In contrast, when T. pyriformis is incubated with any one of a wide variety of added sterols, the biosynthesis of tetrahymanol is inhibited and the added sterol is accumulated by the organism and, in most cases, is converted metabolically into one or more other sterols. Four different types of transformation have been observed: the introduction of Δ 5 , Δ 7 and Δ 22 double bonds, and the removal of ethyl groups, but not methyl groups, from C‐24.