Figure 6: Single molecule load-dependent kinetics as the basis of the ensemble force-velocity relationship in β-cardiac myosin.

a, Unloaded actin sliding velocity measured by in vitro motility assay vs. k₀, the detachment rate at zero load for a single myosin molecule, for the compounds and mutations studied. Linear regression gives a slope of 8.9 nm and R² = 0.81. Note that some points have error bars smaller than the dot. b, The parameter K_s from the loaded motility assay is a measure of load-bearing ability at the ensemble level, while 𝛿 is the load-sensitivity parameter determined at the single molecule level. Pearson correlation −0.94. For clarity, the cluster of data points at the lower right corner are not individually labeled. Motility velocity and K_s values of mutants and dATP are obtained from other studies ^20,25,32,44 (Tomasic I., Liu C., Rodriguez H., Spudich J.A., Bartholomew Ingle S.R., manuscript in preparation). Error bars represent s.e.m.