MYBPC3-c.772G>A mutation alters regulation of the thick filament by accelerating ATP turnover in the C-zone of the sarcomere. (A) Representative image of a human cardiac myofibril illustrating 561-nm illuminated Cy3-ATP (cyan) and 488-nm illuminated α-actinin–containing Z-disks (magenta). (B) Normalized cumulative residence time histogram for all ATP binding events across the entire thick filament for mutation-negative control (squares; N = 2, n = 1,161 events) and MYBPC3-c.772G>A human ventricular myofibrils (circles; N = 1, n = 1,813 events). Dashed lines describe the cumulative exponential fits for both datasets. Cumulative frequency, y axis, is plotted on a logarithmic scale. (C) Percentage of myosin heads quantified to be in the SRX biochemical state in mutation-negative control human myectomy myofibrils and HCM MYBPC3-c.772G>A human myectomy myofibrils. The plot includes all zones and subsarcomeric zones of the thick filament. Data are shown as the mean and 95% CI errors, with significance calculated using bootstrap analysis and indicated by *. Table 2 provides the values used in the graph.