Effect of Tween 80 on lipid vesicle permeability

As part of an examination of procedures for protein/lipid reconstitution we incubated solubilized cytochrome oxidase at different temperatures with preformed vesicles composed of saturated lipids. We observed that the 22Na permeability of these vesicles was increased following such an incubation step, with the maximal effect occurring following incubations at temperatures in the vicinity of the lipid gel to liquid-crystal phase change. However, these permeability changes could be completely duplicated by incubating similar vesicles with concentrations of Tween 80 used to solubilize the extracted oxidase. Thus detergent molecules used to solubilize extracted membrane proteins can induce significant changes in the reconstituting lipid environment and the possibility of such changes must be taken into account when interpreting the properties of the reconstituted lipid/protein system under study.