In all cases, data and fits for the pre-power stroke state are shown in red; data and fits for the post-power stroke state are shown in blue. At saturating (1 mM) ATP concentration (A) both dwell time distributions exhibited single exponential behaviour in line with ADP release being the rate limiting step. The constants for the A state dwell times are given by kA and that for the B state by kB. At lower ATP concentrations, sequential ADP release and ATP binding result in bi-exponential behaviour. At 10 μM ATP (B), both kinetic constants, k1, k2, are almost identical therefore the dwell time distribution is fit to two sequential process with the same rate constant (termed kA for the dwell time of the A state and kB for that of the B state). (C) At 1 μM ATP the process is limited by ATP binding. Data taken at 100 frames/s, we increased the imaging speed to 400 Hz at 1 mM ATP concentration. Total number of steps recorded: 110, 245 and 104, for 1 μM, 10 μM and 1 mM, respectively.