It is planned to study the interaction in solution of myosin moieties with actin using a time-resolved fluorescence depolarization technique. This will involve the study of the effect of nucleotide and actin binding on these moieties as well as the structural consequences of these events. The study of the morphology of S-1 as deduced from X-ray scattering will be extended with greater precision to larger angles in an attempt to define better the shape of S-1. A further project will be to study the electro-optical properties of rods, S-2, and LMM to determine whether the relaxation of the rods can be understood in terms of the relaxation of its constituents. Experiments will continue to attempt to understand the fluorescence polarization field observed around a muscle fiber in such a way that attitude in space of protein moieties can be inferred from measurement and furthermore to attempt to detect cyclic motion of cross-bridge elements. We will pursue preliminary results which indicate that we have experimental evidence of a mole to mole, actin-myosin, binding and a technique which provides an "inter-site" distance at the site where present models call for the S-1 to "roll" on actin. BIBLIOGRAPHIC REFERENCES: X-ray scattering at small angles by solutions of subfragment-1 of myosin. K.M. Kretzschmar, R.A. Mendelson, and M.F. Morales. Biophysical J. Abs. 16: 126a (1976). Affinity of S-1 for F-actin, measured by time-resolved fluorescence anisotrophy. S. Highsmith, R. Mendelson and M.F. Morales. Proc. Nat. Acad. Sci. 73: 133 (1976).