Myosin motors that cannot bind actin leave their folded OFF state on activation of skeletal muscle

Figures

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  Figure 1.. Sarcomere length dependence of the normalized IM3 and the relative intensity of its two central subpeaks (RM3) during isometric contraction. Black circles show experimental data (mean ± SEM; n = 8) from small bundles of fibers from tibialis anterior muscles of Rana esculenta at 4°C (Reconditi et al., 2014). Magenta circles represent the model of Brunello et al. (2007) (in B, magenta points to sarcomere length 2.4 µm coinciding with the experimental data). Green circles represent the modified model in which detached motors make no contribution to the M3 reflection. Blue circles represent the modified model in which 10% of the motors in the no-overlap region are in the folded conformation. See text for details. (A) Normalized IM3 during isometric contraction. (B) Relative intensity of the two central subpeaks during isometric contraction.

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  Figure 2.. Axial profile of the M3 reflection during isometric contraction at sarcomere lengths 2.15 µm and 2.90 µm. Black, experimental profiles reproduced from Reconditi et al. (2014; inset of their Fig. 4 B); magenta, model of Brunello et al. (2007) (green, modified model in which detached motors make no contribution to the M3 reflection). Magenta and green profiles coincide in A. Profiles scaled by the intensity of the lower-angle (LA) central subpeak. RM3 in Fig. 1 is the relative intensity of the higher-angle (HA) and LA central subpeaks. (A) Sarcomere length 2.15 µm. (B) Sarcomere length 2.90 µm. a.u., arbitrary units.

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  Figure 3.. Sarcomere length dependence of the cross-meridional width of the M3 reflection during isometric contraction. The cross-meridional width is measured as the SD of the Gaussian curve used to fit the cross-meridional intensity profile. Mean ± SEM from 10–14 fiber bundles. Calculated from data in Fig. S1 of Reconditi et al. (2014).