Diffusion of H-meromyosin in F-actin plus ATP solution at a very low electrolyte concentration.

The translational diffusion coefficient (D) of H-meromyosin in actin (F-actin) and ATP solution was measured under conditions wherein the actin-activated ATPase activity is close to its maximal value at a very low electrolyte concentration. The results were compared with similar data obtained with 0.1 M KCl, where H-meromyosin and actin were almost completely dissociated. With 0.1 M KCl, it was found that there was no dependence of the D of H-meromyosin on actin concentration. On the other hand, at a very low electrolyte concentration, it was found that the D of H-meromyosin did depend on actin concentration; at a rather high actin concentration (and activation of ATPase), it was slightly larger than at low or zero actin concentrations. This behavior of D at a low electrolyte concentration is interpreted on the assumption that even in solution, H-meromyosin molecules can actively slide on actin filaments due to the ATPase activity.