Table 3.
Ensemble and single-molecule mechanical properties
| Property | WT | S532P | P | F764L | P |
|---|---|---|---|---|---|
| Vactin, μm·s−1 | 4.2 ± 0.7 (20) | 2.4 ± 0.3 (18)* | 0.0001 | 3.4 ± 0.4 (6)* | 0.01 |
| Basal ATPase Vmax, s−1·head−1 | 0.02 ± 0.01 (12) | 0.05 ± 0.3 (5) | NS | 0.02 ± 0.01 (5) | NS |
| Km, μM | 1.2 ± 1.0 (12) | 2.2 ± 2.0 (5) | NS | 1.1 ± 0.6 (5) | NS |
| d, nm | 7.6 ± 2.2 (28) | 5.8 ± 2.4 (39)* | 0.005 | 7.0 ± 2.0 (19) | NS |
| ton, ms | 29 ± 6 (26) | 36 ± 11 (39)* | 0.003 | 29 ± 7 (19) | NS |
| Favg, normalized | 1.0 ± 0.1 (2) | 0.8 ± 0.1 (2) | NS | 0.8 ± 0.1 (2) | NS |
See Materials and Methods for detailed procedures for determination of all parameters. Actin filament velocities (Vactin) are means ± SD from the number of mouse hearts (shown in parentheses). Basal ATPase, ATPase activity in the absence of actin; Vmax ATPase, maximum actin-activated value and Km determined by Michaelis–Menten fit to the ATPase versus actin concentration (see Fig. 2) with the number of hearts in parentheses; d, myosin step size; ton, duration of myosin attachment to actin after the powerstroke, presented as mean ± SD with the number of myosin molecules shown in parentheses. Values of Favg are means ± SE of the estimate as determined from the fit to the mixtures assay data (see Fig. 4).
*Differences were quantified by using a one-way ANOVA with a Student–Neuman–Keuls post hoc test used to locate significant differences at P < 0.05.