Lipid phase separations and intramembranous particle movements in the yeast tonoplast.

The tonoplast of Saccharomyces cerevisiae contains regions depleted of intramembranous particles as the cells enter stationary phase. Freeze-fracture studies on intact cells from this growth stage show that a dispersed particle distribution predominates if the cell temperature is raised to 40 degrees C but that particle-depleted areas prevail at or below the cell growth temperature of 30 degrees C. Tonoplasts of isolated vacuoles also contain particle-depleted regions. Differential thermal analysis of lipids extracted from isolated vacuoles show an endothermic transition which encompasses the cell growth temperature. These results suggest that the tonoplast at this stage contains patches of gel-phase lipid and that these patches correspond to the intramembranous particle-depleted areas of the freeze-fractured tonoplast.