INTRODUCTION OF A METHOD FOR 3-DIMENSIONAL MAPPING OF THE CHARGE MOTION IN BACTERIORHODOPSIN

Electric signals associated with the photocycle of bacteriorhodopsin c arry valuable information about the proton transport process. Photocur rents measured by different experimental methods are interpreted in te rms of intramolecular charge displacements [1,2]. Permanent electrical asymmetry of the sample is considered to be a prerequisite for the de tection of electric signals. The various photoelectric measuring techn iques can be distinguished by the way of achievement of this asymmetry [3]. A common feature of the available methods, however, is that the samples are cylindrically symmetric. Consequently, intramembraneous ch arge displacements can normally be monitored only along the axis of th e membrane normal. We developed a novel method that allows also the de tection of the in-plane components of the charge displacements. Sample s containing oriented purple membrane fragments were used in the exper iments [4], and the rotational symmetry was transiently broken via ani sotropic excitation of the bR molecules by linearly polarized light. K inetics of the normal and in-plane components were measured and interp reted as a result of spatial charge displacements associated with the proton transport process in bacteriorhodopsin.