Incorporation of arachidonic and palmitic acids in large unilamellar vesicles. A comparison of electrical surface parameters

We determine the influence caused by the incorporation, of arachidonic and palmitic acids on the electrical surface parameters (potential, charge dens ity, pK) of large, electrically charged and uncharged, unilamellar vesicles , utilizing fluorescence spectroscopy. The molecular relation of incorporat ed acid varies in the range of 8-24 lipid pairs per acid molecule. The surf ace potential and charge density vary in the range 12-19 mV and 1200-7000 e su cm(-2) (1 esu cm(-2) = 3.335 x 10(-9) C m(-2)). The Delta pK is one-tent h of the pK unit. We found in vesicles without charge (DMPC) that the satur ation ratio for the incorporation of fatty acids is arachidonic : palmitic = 0.6; this relation is inverted in vesicles with charge (soy lecithin), ar achidonic : palmitic = 8, showing an electrical influence on the arachidoni c acid incorporation.