Lipid content and ESR determination of plasma membrane order parameter in Candida albicans sterol mutants.

Sterol intermediates of ergosterol biosynthesis in seven sterol mutants of Candida albicans were determined by gas-liquid chromatography. Only one of them could synthetize ergosterol, while in the others sterol biosynthesis was blocked beyond zymosterol. Alterations in sterol composition were correlated with a slight increase in saturation and a decrease in the chain length of fatty acids, and increases in phosphatidylinositol and phosphatidic acid, and decreases in phosphatidylcholine and phosphatidylserine contents. During exponential growth, as measured on their protoplasts using the intercalated fatty acid spin probe, 5-doxylstearic acid, these single mutants exhibited higher plasma membrane order parameters than their ergosterol-producing parental strain, designated 33 erg+, as follows: erg-12 greater than erg-16 greater than erg-37 much greater than erg-2 greater than erg-20 greater than erg-40 greater than erg-41 greater than 33 erg+. The mutants displayed significantly higher phase-transition temperatures, measured in a reconstituted lipid-water dispersion, than their parental strain.