Figure 4.

Calcium dependence of the (A and B) average working stroke substeps and (C and D) attachment durations for (A and C) myo1b^IQ and (B and D) myo1b^a. (A and B) Ensemble averages of single interactions showing the calcium dependence of myo1b displacements. (C and D) Cumulative frequency distributions of actin-attachment durations for (C) myo1b^IQ and (D) myo1b^a in the absence (•) and presence (■) of 9 μM Ca²⁺_F. Attachment durations were measured for each single-molecule binding event determined by covariance threshold analysis (see Materials and Methods). Solid lines are single exponential functions that were fit to the data (Table 1). Experiments were performed in the optical trap (20 ± 2°C) with 25 μM ATP.