Effect of altered sterol composition on the osmotic behavior of sphaeroplasts and mitochondria of Saccharomyces cerevisiae.

The effect of sterols on the osmotic stability of mitochondrial and plasma membranes of yeast wild-types and mutants that are defective in ergosterol biosynthesis has been studied. Incorporation of the nonfungal sterol, cholesterol, into yeast membranes reduces membrane elasticity which is observed as an increased susceptibility to osmotic lysis. However, the wild-type and nystatin-resistant strains which were examined indicate that qualitative alterations in endogenously generated sterols do not affect resistance to swelling. Although these strains exhibit differences in membrane fluidity, which is influenced by the sterol accumulated by the organisms, the membrane stretching capacity shows no distinct dependence on sterol structure or bilayer fluidity.