Abstract
The theory of optical anisotropy decay r(t) for a protein in a membrane suspension is developed. Our new model describes rotational diffusion of membrane anchored proteins consisting of two different modes occurring simultaneously: one is restricted wobbling of the whole or part of the protein molecule, and the other is rotation of the whole protein about a fixed axis. The anisotropy decay r(t) is characterized by a diffusion coefficient, a cone angle and an angle between the symmetric axis of the wobbling part of the protein and the optical moment of the probe fixed rigidly in the protein. Although the exact r(t) consists of infinite number of exponential functions, an accurate monoexponential plus constant approximation for r(t) is shown to be sufficient for the analysis of experimental data. We derived an analytic expression for the effective relaxation time which appears in this approximation. This treatment may be applicable to complex wobbling plus axial rotation of membrane anchored proteins such as cytochrome b5.
