Table 2. Thin Filament Ca²⁺ Sensitivity for Thin Filaments Reconstituted with cTn and αTm Carrying HCM Mutations^a.

			kobs (s–1)
Tm dimer	pCa50%	h	without Ca2+	with Ca2+	KB
WT-Tm	5.89 ± 0.01	1.23 ± 0.03	2.21 ± 0.07	7.68 ± 0.18	0.40
WT-D175N-Tm	6.00 ± 0.06b	1.20 ± 0.11	2.31 ± 0.01	8.00 ± 0.14	0.40
D175N-Tm	5.97 ± 0.05b	1.24 ± 0.03	2.41 ± 0.06	8.48 ± 0.07	0.41
WT-E180G-Tm	5.92 ± 0.03	1.20 ± 0.09	2.31 ± 0.04	7.58 ± 0.14	0.47
E180G-Tm	6.03 ± 0.06b,c	1.24 ± 0.12	2.71 ± 0.07	8.46 ± 0.16	0.44

^aThe pCa_50% value is the apparent calcium affinity, and h is the Hill coefficient for calcium switching of the thin filaments, both derived from the fit of the Hill equation to the data of panels A and B of Figure 6. All pCa_50% and h values are averages of three measurements with two combined independent Tm and cTn samples. The k_obs values are the observed exponential rate constants of S1 binding to excess thin filaments (2.5 μM ppA, 1 μM hcTn, and 1 μM αTm) in the presence and absence of calcium. k_obs values were derived from observed transients shown in Figure 5. The k_obs rate constants given are averages of two measurements with two independent Tm samples. K_B represents the equilibrium between blocked and closed states of the thin filament. K_B was calculated by using the equation k_obs(−Ca²⁺)/k_obs(+Ca²⁺) = K_B/(1 + K_B).

^bDifferent from the WT value (p ≤ 0.05).

^cDifferent from the E180G heterodimer value (p ≤ 0.05).