pH dependence of the protein orientation in self-assembled bacteriorhodopsin/polycation multilayer films

Abstract

Bacteriorhodopsin (bR) multilayer films were successfully prepared by alternatingdepositions of cationic poly(diallyldimethylammonium chloride) (PDAC) polyelectrolyte and purple membrane (PM). The advantage of the method when compared to other thin film techniques is its simplicity to prepare large selfassembled films. The orientations of the bR molecules in the films were studied by a transient photovoltage method. The polarity of the photoresponse signals showed that in basic conditions the cytoplasmic side of PM was adsorbed onto the polyelectrolyte layer, whereas in acidic conditions the extracellular side was adsorbed onto the polyelectrolyte layer. The photocycle of the bR in the films was studied by usingthe conventional flash photolysis method. The photochemical behavior of bR in dry polycationic films was similar to that in other types of dry films and the intermediate lifetimes were almost independent of the protein orientation.