Alteration in Membrane Fluidity and Lipid Composition, and Modulation of H+-ATPase Activity in Saccharomyces Cerevisiae caused by Decanoic Acid

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Abstract
Decanoic acid, a lipophilic agent, inhibitedin vitrothe plasma membrane H+-ATPase ofSaccharomyces cerevisiaegrown in YPD medium. Conversely, when decanoic acid (35 μM) was present in the growth medium, the measured H+-ATPase activity was four times higher than that of control cells.Km, and pH and orthovanadate sensitivity were the same for the two growth conditions, which indicated that H+-ATPase activation was not due to conformational changes in the enzyme. The activation process was not entirely reversible which showed that plasma membrane H+-ATPase activation is due to several mechanisms. 1,6-diphenyl-1,3,5-hexatriene anisotropy performed on protoplasts from cells grown in YPD revealed that as decanoic acid concentration was increased, anisotropy significantly 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 any fluidifying effect when increased concentrations of decanoic acid were added. Chemical analysis of cell membrane lipid composition revealed a modification in the distribution of the phospholipid fatty acids and sterols in cells grown in the presence of 35 μM decanoic acid compared 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.