Cooperativity of an acid phospholipid reaction with basic hydrophobic polyelectrolytes or with the apoprotein proteolipid from myelin: I. Surface pressure, surface potential, and recombination studies with monolayers

Abstract

For two types of mixed monolayers the surface pressure and surface potential have been measured as a function of their composition. They were formed by spreading of an acidic phospholipid and either a basic polysoap or a basic hydrophobic protein from myelin. The reaction was followed by using a radioactive counterion as an indicator. It was found that with the polysoap, highly charged by dissociation, the reaction with the acidic lipid was cooperative, contrary to the case of the protein which was not highly charged. For both, however, screening of the electrostatic repulsion between the ionized groups of the polyions by the lipid charge appears as a “condensation” of the polyions and of the lipid. Models are suggested to interpret this condensation and the mutual structuration of the polyions and of the lipid molecules. They are extended to biological membrane structures in the absence or in the presence of applied force or electrical fields.