Buffer-induced changes of purple membrane surface electric properties: an electro-optical study

Buffer-induced alteration of the purple membrane electric dipole moments and electrokinetic charge was studied by electric light scattering and microelectrophoresis. The permanent dipole moment and electrophoretic mobility of purple membranes change in opposite direction in presence of 'P'- and 'N'-type buffer molecules, shown to produce 'positive' and 'negative' additional components to the bR light-induced charge displacement current. It is concluded that the two types buffer molecules distribute differently on the membrane surfaces, depending on their protonation state, as a result of different interaction with the membrane cytoplasmic and extracellular surfaces.