FIGURE 2.

ATPase assay using reconstituted thin filament-myosin-S1. ATPase activity normalized relative to non-labeled non-cross-linked troponin in presence of 0.7 mm Ca²⁺ n = 4 ± S.E. The assay was performed in higher salt (21 mm MOPS, pH 7.0, 105 mm NaCl, 5.25 mm MgCl, and 1 mm ATP) to keep human troponin in solution. X-link Ca²⁺, cross-linked either with or without Ca²⁺; NA, not applicable; Assay Ca²⁺, assay condition with or without Ca²⁺. A, S5C mutant, assayed with human troponin and S5C troponin I mutation. *, p value = 0.0002; ^#, p value = 0.005. B, I19C mutant, assayed with human troponin and I18C troponin I mutation. *, p value < 0.0001; ^#, p value < 0.0001; **, p value = 0.0044.