Depolarization spectrum of diffracted light from muscle fiber. The intrinsic anisotropy component.

The depolarization signal of the diffraction patterns from muscle fibers includes information that differs from that of transmission birefringence experiments. Although both the birefringence studies and the phase shift studies of Yeh et al. (Yeh, Y, and G. Pinsky, 1983, Biophys. J., 42:83-90; Yeh, Y., M. E. Corcoran, R. J. Baskin, and R. L. Lieber, 1983, Biophys. J., 44:343-351) include inseparable intrinsic and form contributions, the present analysis shows that the magnitude of the E-field components of diffracted light is affected only by the intrinsic contribution. We have analyzed the amplitude portion of the data of which the phase shift portion had previously been reported (Yeh, Y., M. E. Corcoran, R. J. Baskin, and R. L. Lieber, 1983, Biophys. J., 44:343-351). For the relaxed-to-rigor transition, these field amplitudes also exhibit changes when ATP concentration is decreased. The observed decrease in optical depolarization upon rigor is consistent with the idea that optically anisotropic elements move away from the myosin thick filament under such conditions.