Figure 6.

Step-frequencies for cardiac (a) and skeletal (b) actin with frictional loading indicated from 0 to 9 pN. Curves are from simulation of the corresponding event–velocity histograms in figure 5 and as described in Methods. Errors are standard deviations for the 8–16 replicates indicated for each species in figure 5. Leading step-size choice for βmys moving cardiac actin is always the long (blue) step-size. By contrast, βmys moving skeletal actin is always the intermediate (green) step-size. These selections reflect competitive regulation of the myosin mechanical characteristics by the ELC ratchet and lever arm strain mechanisms.