Time-resolved fluorescence polarization from ordered biological assemblies

We calculate the time dependence of the polarized fluorescence signal from fluorescent-labeled elements of a biological assembly that are rotationally diffusing in an arbitrary three-dimensional angular potential. We have formulated this calculation using the model-independent description of the angular potential wherein the angular potential is described by an expansion in a complete set of orthonormal functions with the expansion coefficients (or order parameters) determined by time-independent methods (Burghardt, T. P., 1984, Biopolymers, 23:2382–2406). We have applied the calculation to fluorescent-labeled myosin cross-bridges in relaxed muscle fibers. In a related paper we describe the experimental observation of the myosin cross-bridges rotationally diffusing in an angular potential (Burghardt, T. P., and N. L. Thompson, 1985, Biochemistry, 24:3731–3735).