LIMITED ROTATIONAL DIFFUSION CAUSED BY FRICTIONAL INTERACTION AMONG PURPLE MEMBRANE-FRAGMENTS IN A HIGHLY CONCENTRATED PURPLE MEMBRANE SOLUTION SPREAD OVER A WATER-SURFACE

Purple membrane (PM) fragments spread over an air-water interface show both preferential orientation and reverse orientation (i.e., the cyto plasmic side of bacteriorhodopsin being oriented toward the water and toward the air, respectively). We used a spectroscopic surface denatur ation quantifying technique and a current-measurement technique to eva luate the ratio of the amount of preferentially oriented bacteriorhodo psin (BR) to the amount of all BR in a PM film. This ratio decreased a s the initial coverage (the ratio of the total area of all the PM frag ments spread on the air-water interface to the area of the air-water i nterface before the PM was spread over the interface) increased, when the initial coverage was high (more than 0.3). We concluded that this decrease was due to the limited rotational diffusion caused by frictio nal interaction among PM fragments in a highly concentrated PM solutio n spread over a water surface. (C) 1997 Elsevier Science S.A.