ON STABILITY OF MYOSIN FILAMENTS

Previous work has established that myosin molecules are in rapid equilibrium with a single, high molecular weight polymeric species (mol wt 50-60 X 106) in the pH range 8-8.5 (KCl concentration 0.13-0.20 M). In the present study the equilibrium constant of this myosin-polymer system has been evaluated from sedimentation velocity experiments as a function of ionic strength, pH, temperature, and hydrostatic pressure. Results indicate that the transformation of myosin monomer into polymer is accompanied by the release of 11 moles of KCl/monomer unit while approximately 0.68 mole (per monomer) of hydrogen ion is absorbed. The equilibrium constant is independent of temperature (over the range 1-16°), but is markedly affected by hydrostatic pressure. The dependence of the equilibrium constant on the hydrostatic pressure generated in high-speed sedimentation experiments has been evaluated and from these studies a positive volume change of 380 cc/mole of monomer was estimated for the association process. These results, when taken in conjunction, suggest that a maximum of 25 ionic bonds (per myosin molecule) is formed when the monomeric units associate to form the ordered macrostructure of the polymer. © 1968, American Chemical Society. All rights reserved.