Reversible cryogenic alteration of the ultraviolet absorption spectra of the olefinic bonds in lipid membranes.

Abstract

In earlier studies it was found that the association of basic polypeptides with lipid vesicles drastically altered ultraviolet absorption by the olefinic bonds of the lipid. Such an effect suggested that the polypeptide was increasing the polarity of the chromophore environment by either direct interaction with the acyl chains or by inducing their hydration. It is reported here that freeze-thaw cycling, which was expected to allow hydration of the olefinic-bond region of the membranes, caused the same spectral alteration as vesicle interaction with basic polypeptides. When these vesicles were subsequently placed under conditions that would be expected to accelerate the escape of water entrapped within the membranes (i.e., by placing them under vacuum or adding sucrose to establish a high osmotic gradient to their exterior), the absorption spectrum was rapidly restored to that for olefinic bonds in a nonpolar environment. Since placing the polylysine- dioleoylphosphatidylcholine (DOPC) vesicle interaction product under the same conditions restored the spectral intensity, at 190 nm, to between 80 and 85% of that for the lipid in a nonpolar environment, it seems that a major effect of polylysine on DOPC membranes may be though induction of hydration of their interior.