Impact of the E525K mutation on β-cardiac myosin motility. Velocity Index versus surface occupancy for WT and E525K 2HEP, 15HEP, and 25HEP constructs. WT data and fitted curves from Fig. 6 b. All three E525K constructs were not significantly different than their WT controls (2HEP, P = 0.75; 15HEP, P = 0.75; 25HEP, P = 0.87). Dashed curves are the least squared error model fits to the Velocity Index versus surface occupancy relations in order to estimate the %IHM/SRX for the various E525K constructs (see legend in figure). The predicted %IHM/SRX for all of the E525K mutants are no different than WT. All in vitro motility experiments performed in low salt (25 mM KCl). Data points are presented as mean ± SD of at least three experiments from separate protein preparations.