Abstract
Cellular and membrane systems that are well defined with respect to lipid compositions were obtained from cultures of unsaturated fatty acid auxotrophs of Saccharomyces cerevisiae supplemented with specific 18-carbon unsaturated fatty acids. Lipophilic spin labels were used to probe the physical state of the lipids in the resulting membrane systems. Arrhenius plots for the O 2 uptake of cells grown on lactate, and for the motion of a spin label in the lipid moieties of these cells display discontinuities at the same temperature. The characteristic temperature which defines the change in slopes in these plots is dependent upon the physical characteristics of the unsaturated fatty acid that supplemented a given culture. It is inferred that the changes in slopes originate from temperature-dependent changes in the physical state of lipid moieties. Adamantane, a hydrophobic quasi-spherical molecule, was used as a liphophilic perturber to cooperatively hinder the axial ordering of phospholipid alkyl chains. Experimental evidence indicates that adamante lowers the transition temperatures detected from the temperature dependence of the motion of spin labels and from the Arrhenius plots of O 2 uptake. Additional experiments were carried out to determine the effect of other perturbing molecules and of mixtures of unsaturated fatty acids on the temperature dependence of spin-label motion. The approximate coincidence of transition temperatures in both O 2 uptake and spin-label experiments infers that membrane-dependent physiological functions are dependent upon the physical state of membrane lipids.
Published Version
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