Change of Lecithin Aggregation Due to Valinomycin‐Lipid Interaction

Abstract

AbstractValinomycin added to a suspension of lecithin vesicles with chlorophyll a or b incorporated into their membranes induces slight changes in the absorption spectrum of chlorophyll. The analysis of these changes revealed that this effect is not associated with the ionophoric properties of valinomycin but indicates a valinomycinlecithin interaction. As a consequence, the aggregational state of the lecithin molecules is altered in a domain which comprises about 40 lipids around one valinomycin molecule. The ability of the chlorophylls to detect different lipid aggregations arises from their solvatochromic behaviour. Using spectroscopic data for chlorophyll in different solvents, it could be inferred that a change in electrostatic interaction is the main reason for the difference of the spectrum of chlorophyll embedded in lecithin of different aggregational states. This interaction originates from a strong electric field associated with the polar moieties of the lipids which is much larger than the field imposed by transmembrane potentials. Hence the absorbance changes of chlorophyll due to such potentials are rather small compared to those induced by valinomycin.