Cross-correlated photon scattering during the photocycle of bacteriorhodopsin

Changes in the ultraviolet light scattering from a suspension of purple membrane fragments were detected during the photocycle of bacteriorhodopsin with a cross-correlation method. The scattered light intensity from a suspension of membrane fragments containing the protein bacteriorhodopsin was measured on a logarithmic time scale of 1 microsecond to 0.1 s at pH 4.6 after the photocycle was initiated with a polarized 532-nm laser flash. A simple model of curved sheets with positive and negative changes in the curvature is used to describe the observed light scattering changes. A detailed mathematical derivation of the model as well as the pictorial description are given. The changes in curvature of the membrane fragment are more than likely driven by the protein during the photocycle and are observed to have at least two time-resolved components, each changing the curvature of the fragment with an opposite sign.