Optical properties of myofibril and actomyosin suspensions. 1. Angular dependence of light scattering by myofibril suspensions and its changes under myofibril contraction.

The angular dependence of light scattering by myofibril suspensions has been measured within the angle range of 0.05 degrees and 160 degrees at different suspension concentrations and wavelengths. Angular diagrams appear to be highly asymmetry, and extended forward in the direction of the primary light propagation. A suspension with the concentration of 0.1 mg/ml at 550 nm scatters, for example, no less than 90% light at angles of less than 6 degrees. The scattering diagram becomes less asymmetric upon increasing the suspension concentration and decreasing the wavelength of the light. Upon addition of MgATP in the presence of Ca2+, a myofibril suspension undergoes two kinds of optical change, namely, fast ones corresponding to myofibril contraction, and slow ones correlating with the subsequent aggregation of the contracted myofibrils. Fast changes are believed to be due to the increase of the refractive index of the contracting myofibrils, and slow changes to the increase in the size of the suspension particles resulting from aggregation. Light scattering by myofibril and actomyosin suspensions seems to be due not only to the particle as a whole, but also to its internal structure.