Quasielastic light scattering study of solutions of synthetic myosin filaments

Autocorrelation functions of the intensity fluctuations of light quasielastically scattered from solutions of synthetic myosin filaments were measured by means of single photon counting. The angular distribution of the total scattering intensity was measured simultaneously, and a supplementary investigation of depolarized light scattering was also performed. The light scattering data were analyzed based on the length distributions of synthetic filaments observed under an electron microscope. The results showed that synthetic filaments in a solution behave essentially as rods. The hydrodynamic frictional coefficient of synthetic filaments, however, was shown to be about twice as high as would be expected if the filaments took a ‘compact’ conformation. This strongly suggests the existence of certain projections which are widely spread from the filament backbone in a solution. The molecular weight of the synthetic filament was calculated using the observed values of the translational diffusion coefficient and the sedimentation coefficient. The number of myosin molecules per 14.3 nm repeat was shown to be six or greater, which suggests that synthetic filaments lack an effective width-limiting mechanism which is presumed in the native thick filament. Additions of Ca²⁺, Mg²⁺ and ATP, alone or in combination, have been shown to cause no notable changes in the light scattering profile of synthetic filaments.