Table 4.

Measured parameters of Cross-bridges. *P value ≤ .05 compared to nfTm; **P value ≤.01 compared to nfTm; else, P value > .05. Other than rigor stiffness, all parameters were measured in the standard activating solution. T _m is the steady-state active tension. Tension and stiffness were normalized against the actin filament tension (T _ac) in the standard activating solution at 25°C (T _ac = 9.0 ± 0.9 kPa, ± SEM, N = 52). To deduce f _min, 5 frequency points around the minimum |Y(f)| are fitted to the cubic equation with 4 constants. 2πb corresponds to the rate constant of phase 3, and 2πc corresponds to that of phase 2 of step analysis [32]. In all experiments, temperature was 25°C, ionic strength 200 mM, and pH 7.00. The rigor stiffness was measured at 100 Hz. The data were individually fitted to respective equations, averaged, and tabulated with ± SEM. ^†Data based on Lu et al. [13].

	nfTm	∆2Tm	∆3Tm	Acetyl Tm†	Units
Number of expts.	15	17	18	9
Tension (T m)	1.51 ± 0.28	1.65 ± 0.29	0.91 ± 0.08*	1.65 ± 0.24	T ac
Y ∞	103 ± 24	103 ± 14	71 ± 5	89 ± 14	T ac
T m/Y ∞	1.56 ± 0.08	1.58 ± 0.14	1.31 ± 0.10*	1.91 ± 0.10**	%L 0
Rigor stiffness	166 ± 11	201 ± 19*	249 ± 59	159 ± 23	T ac
2πf min	8.6 ± 0.4	7.4 ± 0.4	7.2 ± 0.4**	7.6 ± 0.6	s−1
2πb	6.2 ± 0.4	6.3 ± 0.5	4.7 ± 0.4**	7.1 ± 1.0	s−1
2πc	28 ± 1	28 ± 2	36 ± 3**	41 ± 4**	s−1
H	49 ± 11	51 ± 9	34 ± 4	28 ± 6*	T ac
B	56 ± 20	55 ± 13	22 ± 2*	29 ± 6	T ac
C	110 ± 34	107 ± 17	58 ± 3	90 ± 13	T ac