Figure 7. Effect of the central helix mutations on the specific activities and Ca²⁺ sensitivities of actomyosin ATPase.

Panel A shows the specific actomyosin ATPase activity of the cTn, cTn^D87A/D88A, or cTn^{E94A/E95A/E96A} complexes reconstituted into thin filaments (in the presence of myosin S1) at pCa 9.0 (open bars) or pCa 4.5 (bars filled with slanted lines). The cTnC proteins (with C35S/T53C/C84S substitution) were labeled with IAANS at Cys⁵³. Each data point represents a mean ± SE of three separate experiments (each carried out in triplicate). Values marked with * are significantly different from the control values at pCa 9.0 (p< 0.05). Values marked with ** are significantly different from the control values at pCa 4.5 (p<0.05). Panel B shows the Ca²⁺ dependent activity of actomyosin ATPase for the cTn (■), cTn^D87A/D88A (●), or cTn^{E94A/E95A/E96A} (○) complexes reconstituted into thin filaments (in the presence of myosin S1) as a function of pCa. Each data point represents a mean ± SE of at least three separate experiments (each carried out in triplicate). Data sets were individually normalized for each mutant cTn complex reconstituted into thin filaments (in the presence of myosin S1), and fit with logistic sigmoid.