Light scattering changes during the photocycle of bacteriorhodopsin.

Spectroscopic measurements on purple membrane suspension are disturbed by the light scattering of the particles. Systematic study of the scattered light leads to the observation that scattering changes during the photocycle, and that this change depends on the flash polarization, pH, and the solvent viscosity. A theoretical model is given to explain the experimental data. The model asserts that the purple membranes are bent and, during the photocycle, the degree of bending varies due to the conformational change of the bacteriorhodopsin molecules.