State of myosin in solution: Electric birefringence and dynamic light-scattering studies

Abstract Myosin and heavy meromyosin solutions have been studied at high ionic strengths by means of relaxation techniques such as polarized dynamic light-scattering and electric birefringence. Contrary to translational parameters, rotary diffusion constants were found to be independent of protein concentration and depend only slightly on buffer phosphate concentration; the electrical polarizability of both molecules is mainly due to a permanent dipole moment. Considering the results, five of the six association models proposed by Harrington & Burke (1972) have been excluded. Thus, the only remaining possibilities are either a side-to-side parallel dimeric form, which it was not possible to exclude formally, or the quasi-exclusive presence of the monomeric species. On the basis of the hydrodynamic parameters, the dimensions and flexibility of myosin and heavy meromyosin molecules are discussed, particularly in relation to the model proposed by Garcia de la Torre & Bloomfield (1980), which best fits our results.