SELF-ASSOCIATION PROCESSES INVOLVING ANTHRACENE LABELED PHOSPHATIDYLCHOLINES IN MODEL MEMBRANE

When studying lipid-lipid or lipid-protein interaction in membranes, t he correct interpretation of data obtained when using fluorescent phos pholipid probes requires the best possible knowledge of probe behaviou r in phosopholipid membranes. Analysis of the translational dynamics a nd photochemical properties of the anthracene-labeled phosphatidylchol ine (EAPC) shows that a self-association process occurs with this prob e in the membrane at the ground state. This anthracene self-associatio n is characterized and leads to a hypochromic effect which has been st udied by means of ultraviolet absorption spectroscopy in unilamellar e gg-yolk phosphatidylcholine (EggPC) vesicles. A model with indefinite linear self-association, in which each step has the same equilibrium c onstant, best describes the data. The equilibrium constant was found t o be in the 300-500 M(-1) range and the complex lateral distribution p attern of EAPC in model membranes, which results from this self-associ ation process, is characterized and seems to be mainly controlled by t he amount of EAPC incorporated into the lipid bilayer.