Protozoa, sterols

Biotin is a growth factor for many bacteria, protozoa, plants, and probably all higher animals. In the absence of biotin, oxalacetate decarboxylation, oxalosuccinate carboxylation, a-ketoglutarate decarboxylation, malate decarboxylation, acetoacetate synthesis, citrulline synthesis, and purine and pyrimidine syntheses, are greatly depressed or absent in cells (Mil, Tl). All of these reactions require either the removal or fixation of carbon dioxide. Together with coenzyme A, biotin participates in carboxylations such as those in fatty acid and sterol syntheses. Active C02 is thought to be a carbonic acid derivative of biotin involved in these carboxylations (L10, W10). Biotin has also been involved in... 

Although the composition and structure of mammalian (mainly erythrocyte and myelin) membranes has received extensive study, little attention has been paid to the membranes of yeasts, fungi and protozoa. Extraction of lipids from these organisms suggest similarities in overall structure, although cholesterol, which has an almost universal distribution in mammalian cells was replaced by other sterols, e.g. ergosterol (14) in yeasts and fungi [126]. The presence of... 

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