Inactive fatty acids are unable to flip-flop across the lipid bilayer

Free fatty acids (FA) mere found which did not acidify liposome interior, This is interpreted as their inability to rapidly flip-flop across the lipid bilayer, However, they were able to partition in lipids as detected directly using HPLC or from the shift of their equilibrium binding to acrylodated intestinal binding protein (ADIFAB) in the presence of vesicles, Various bipolar FA, such as 12-hydroxylauric acid, dicarboxylic acids, or FA with benzene ring at the tail mere found to be inactive in this may, A phenomenon of shielding, where an additional alkyl chain or non-polar group can restore the flip-flop activity, is described. (C) 1997 Federation of European Biochemical Societies.