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

Abstract

We determine the influence caused by the incorporation, of arachidonic and palmitic acids on the electrical surface parameters (potential, charge density, pK) of large, electrically charged and uncharged, unilamellar vesicles, utilizing fluorescence spectroscopy. The molecular relation of incorporated acid varies in the range of 8–24 lipid pairs per acid molecule. The surface potential and charge density vary in the range 12–19 mV and 1200–7000 esu cm⁻² (1 esu cm⁻² = 3.335 × 10⁻⁹ C m⁻²). The ΔpK is one-tenth of the pK unit. We found in vesicles without charge (DMPC) that the saturation ratio for the incorporation of fatty acids is arachidonic: palmitic = 0.6; this relation is inverted in vesicles with charge (soy lecithin), arachidonic: palmitic = 8, showing an electrical influence on the arachidonic acid incorporation.