The D65A mutation in cTnC inhibits activation of troponin in the presence of calcium. (A) Normalized steady-state fluorescent emission change of purified and IANBD-labeled WT (black) and D65A (red) cTnC at increasing concentrations of calcium. (B) Force generation of permeabilized porcine myocardium strips with exchanged rat WT or D65A full troponin complex at submaximal (pCa 5.8) and maximal (pCa 4.5) calcium.