CHARACTERISTICS OF FPS1-DEPENDENT AND FPS1-INDEPENDENT GLYCEROL TRANSPORT IN SACCHAROMYCES-CEREVISIAE

Eadie-Hofstee plots of glycerol uptake in wild-type Saccharomyces cere visiae W303-1A grown on glucose showed the presence of both saturable transport and simple diffusion, whereas an fps1 Delta mutant displayed only simple diffusion. Transformation of the fps1 Delta mutant with t he glpF gene, which encodes glycerol transport in Escherichia coli, re stored biphasic transport kinetics, Yeast extract-peptone-dextrose-gro wn wild-type cells had a higher passive diffusion constant than the fp s1 Delta mutant, and ethanol enhanced the rate of proton diffusion to a greater extent in the wild type than in the fps1 Delta mutant. In ad dition, the lipid fraction of the fps1 Delta mutant contained a lower percentage of phospholipids and a higher percentage of glycolipids tha n that of the wild type. Fps1p, therefore, may be involved in the regu lation of lipid metabolism in S. cerevisiae, affecting membrane permea bility in addition to fulfilling its specific role in glycerol transpo rt. Simultaneous uptake of glycerol and protons occurred in both glyce rol-and ethanol-grown wild-type and fps1 Delta cells and resulted in t he accumulation of glycerol at an inside-to-outside ratio of 12:1 to 1 .5:1, Carbonyl cyanide m-chlorophenylhydrazone prevented glycerol accu mulation in both strains and abolished transport in the fps1 Delta mut ant grown on ethanol, Likewise, 2,4-dinitrophenol inhibited transport in glycerol-grown wild-type cells. These results indicate the presence of an Fps1p-dependent facilitated diffusion system in glucose-grown c ells and an Fps1p-independent proton symport system in derepressed cel ls.