DYNAMIC LIGHT-SCATTERING FROM SEMIDILUTE ACTIN SOLUTIONS - A STUDY OFHYDRODYNAMIC SCREENING, FILAMENT BENDING STIFFNESS, AND THE EFFECT OFTROPOMYOSIN TROPONIN-BINDING/

Quasi-elastic Light scattering (QELS) is applied to investigate the ef fect of the tropomyosin/ troponin complex (Tm/Tn) on the stiffness of actin filaments. The importance of hydrodynamic screening in semidilut e solutions is demonstrated. A new concentration dependent-expression for the dynamic structure factor g(k, t) of semiflexible polymers in s emidilute solutions is used to analyze the experimental QELS data. A c oncentration independent value for the bending modulus kappa is thus o btained. It increases by 50% as a consequence of Tm/Tn binding in a 7: 1:1 molar ratio of actin/Tm/Tn. In addition a new expression for the i nitial slope of the dynamic structure factor of a semiflexible polymer is used to determine the effective hydrodynamic diameter of the actin filament. Our results confirm the general relevance of the concept of (intrinsic) semiflexibility to polymer dynamics.