The viscosity and lipid composition of the plasma membrane of multiple drug resistant and sensitive yeast strains.

Four different plasma membrane preparations were isolated from multiple drug resistant and sensitive isolates of two isogenic groups of Saccharomyces cerevisiae strains: zymolyase ghosts, concanavalin A ghosts, pH 4 nonaggregated vesicles, and sucrose-gradient purified vesicles. The viscosities of these preparations were determined by the use of a fluorescence polarization technique with 1,6-diphenyl-1,3,5-hexatriene. The viscosities of all four membrane preparations within an isogenic set were the same for resistant and sensitive strains. A comparison of the viscosity of zymolyase ghost liposomes showed that zymolyase ghost (glyco) proteins of resistant and sensitive strains had the same effect on viscosity. There was no difference between resistant and sensitive isolates in the mole concentration of the following lipid classes extracted from zymolyase ghosts: phospholipid, sterol, sterol ester, triglyceride, diglyceride, and free fatty acid. The fatty acid distribution of esterified and free fatty acids and the distribution of nine phospholipids was the same in zymolyase ghosts from sensitive and resistant strains. It was concluded that multiple drug resistance does not result from an alteration in plasma membrane viscosity or lipid composition.