Controlling the Orientation of Purple Membrane Fragments on an Air/Water Interface by a New Method of Direct Electric Field Application during Purple Membrane Spreading

Abstract

The orientation of purple membrane (PM) fragments on an air/water interface was controlled by a direct electric field applied across the interface during spreading of a PM solution. We call this the direct electric field application Langmuir-Blodgett (LB) technique, and found it effective in increasing the population of preferentially oriented PM fragments at the interface. Using this technique with an electric field exceeding 4 kV/cm and an initial coverage C i of 0.2 (i.e., the ratio of the surface area of the air/water interface covered by PM fragments to the total surface area of the interface before the PM was spread over the interface), we produced a PM LB film in which all the constituent PM fragments were preferentially oriented. We successfully demonstrated that this technique is a powerful tool for producing LB films in which proteins are perfectly oriented (i.e., all the constituent PM fragments are preferentially oriented).