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.