FIGURE 8.
Effects of R95C mutation on Tm·Tn function. Velocities of moving filaments (A) and percentage of filaments moving at uniform speeds (B) of RhPh-labeled WT, R95C filaments, and cofilaments over HMM surfaces were measured in the presence of Tm·Tn and various Ca2+ concentrations (pCa) at 25 °C. The Hill coefficient, pCa50, maximum velocity (Vmax (μm/s)), and maximum percentages of filaments moving at uniform speeds (Fmax (%)) were obtained by fitting each data set to the Hill equation (the parameters used are given in Table 2). Error bars indicate S.D. The differences of velocities and percentages of filaments moving at uniform speeds at pCa 6.7 between each pair of WT filaments and R95C filaments or cofilaments were significant (p < 0.05, t test). A significant fraction of filaments was not moving at intermediate pCa, and to avoid very large S.D., those stalled filaments were excluded from velocity analysis (30). However, this procedure resulted in excessive high velocity at high pCa if a very small number of filaments moved at velocities above the cutoff, even though the vast majority of the filaments had stalled. Therefore, those data points were excluded from fitting to the Hill equation, and zero values were used instead at those data points, which are shown in parentheses. Shown here is a representative of three independent experiments.