Figure 6. Effect of disease-related protein modifications on the rate of Ca²⁺ association to the thin filament.

Panel A shows the kinetic traces (an average of 3 to 5 individual traces collected at least 9 times) observed for Ca²⁺ association to thin filament bound control at 5 µM, 10 µM and 20 µM Ca²⁺ ([Ca²⁺] after mixing). Panel B shows the kinetic traces (an average of 3 to 5 individual traces collected at least 9 times) observed for Ca²⁺ association to thin filament bound TnI(1-192) at 2.5 µM, 5 µM and 10 µM Ca²⁺. The rate of the fluorescence increase when Ca²⁺ associates with the thin filament was fit with a single exponential to calculate the observed rate (k_observed). All complexes consist of the full length Tn subunits of , TnI and TnT, except for ischemic related truncated TnI (1-192). The disease related modification is either in TnI or TnT, in either case, the other protein (TnT or TnI) was wild type. Panel C shows the plots of k_observed versus [Ca²⁺] for thin filament bound control (□) and TnI (1-192) (). The rate of Ca²⁺ association to the thin filament was obtained by calculating the slope of a linear fit to the data. Panel D shows the plots of k_observed versus [Ca²⁺] for thin filament bound TnI R192H (▵), TnI D190H (▽), TnT ΔK210 (⋆), and TnT R131W (○).