Figure 3.

Power stroke size of β-cardiac myosin. A and B, the histogram with displacement events measured at 5 μM ATP for βMII and at 10 μM ATP for SolM-II. The average stroke size was estimated by using shift-of-histogram method (74). Least squares fitting of event distribution with Gaussian function yields average power stroke, δ = 5.32 ± 0.16 nm and 6 ± 0.19 nm for βM-II and SolM-II, respectively. p ˂ 0.05 with unpaired t test. B–E, ensemble averaging of the individual AM-association events. The beginning and the end of the several individual AM-binding events were synchronized and fitted with single exponential functions to estimate the substeps. The beginning is shown as a forward fit (red points) and the end (green points) as a backward fit. Average stroke size (δ) and displacement size corresponding to the first and second stroke is indicated as δ1 and δ2, respectively. K₁—reaction rate for the ADP dissociation and K₂—ATP induced AM dissociation at respective ATP concentration. K₂ = 4 s⁻¹ and 10.2 s⁻¹ at 1 and 5 μM ATP, respectively. For 1 μM ATP, N = 16, n = 987; for 5 μM ATP, N = 7, n = 500. For SolM-II at 10 μM ATP, N = 11, n = 520. N = Number of molecule, n = number of events. Important to note that for ensemble averaging, the AM attachment events with a lifetime of minimum 0.05 s or longer were selected. The method is described in detail in Veigel et al. (24) and Blackwell et al. (25)