EFFECT OF THE CHANGE IN LIPID-COMPOSITION OF PLASMA-MEMBRANES FROM SACCHAROMYCES-CEREVISIAE DUE TO MUTATION ON THE PHASE-TRANSITION AND MIXING BEHAVIOR OF LIPIDS FRACTIONS

Mutation of Saccharomyces cerevisiae leads to an alteration of the siz e and surface structure of the mutant cell. These phenomena are correl ated with change in the lipid composition and hence membrane fluidity of the plasma membranes. Such alterations are in the fatty acyl consti tuents of phospholipids and glycolipids and include changes in the sat uration or length of fatty acyl chains. Simultaneously, the ''melting point'' of phospholipid fractions, i.e. the temperature of the ordered -disordered phase transition and mixing behavior, changed. Consequentl y calorimetry on isolated phospholipid fractions extracted from plasma membranes is a useful analytical method to demonstrate directly such phase transitions and change in the mixing behavior of the cellular li pid fractions in connection with mutation. A correlation between the a lteration of the lipid composition in the plasma membrane of strains o f S. cerevisiae S 288 and its mutant VY 1160 is discussed.