Relationship between the flexibility and the motility of actin filaments: Effects of pH

Both the sliding velocity of fluorescently labeled actin filament and its persistence length as an index of the bending flexibility of the filament were examined in the motility assay as varying the pH values of the solution for preparing actin filaments. When the pH value was varied from 5.0 to 9.0 in the solution in which actin filaments were formed from the constituent monomers, the motile performance of Mg2+ bound actin filaments (Mg–F-actin) was apparently suppressed compared to the case of Ca2+ bound ones (Ca–F-actin). The persistence length for Ca–F-actin gradually increased with the increase of the pH value while the similar length for Mg–F-actin remained rather independent of the value. The largest sliding velocity of the filament, on the other hand, obtained at the persistence length of roughly 6 μm for both cases of Mg–F-actin and Ca–F-actin.