ALTERATION IN MEMBRANE FLUIDITY AND LIPID-COMPOSITION, AND MODULATIONOF H-ATPASE ACTIVITY IN SACCHAROMYCES-CEREVISIAE CAUSED BY DECANOIC ACID()

Decanoic acid, a lipophilic agent, inhibited in vitro the plasma membr ane H+-ATPase of Saccharomyces cerevisiae grown in YPD medium. Convers ely, when decanoic acid (35 mu M) was present in the growth medium, th e measured H+-ATPase activity was four times higher than that of contr ol cells. K-m, and pH and orthovanadate sensitivity were the same for the two growth conditions, which indicated that H+-ATPase activation w as not due to conformational changes in the enzyme. The activation pro cess was not entirely reversible which showed that plasma membrane H+- ATPase activation is due to several mechanisms. 1,6-diphenyl-1,3,5-hex atriene anisotropy performed on protoplasts from cells grown in YPD re vealed that as decanoic acid concentration was increased, anisotropy s ignificantly decreased, i.e. membrance fluidity increased. Cells grown in media containing decanoic acid exhibited greater membrane fluidity compared with control cells. Furthermore, these cells did not show an y fluidifying effect when increased concentrations of decanoic acid we re added. Chemical analysis of cell membrane lipid composition reveale d a modification in the distribution of the phospholipid fatty acids a nd sterols in cells grown in the presence of 35 mu M decanoic acid com pared with control cells. Our results support the view that the plasma membrane H+-ATPase activation induced by decanoic acid is correlated with an alteration in membrane lipid constituents.