FIGURE 1.
Arrangement of a unit cell used in the model. A segment of thin filament, including actin monomers, tropomyosin strand, TM, and 2 troponin molecules, TN, with a stereospecifically attached myosin head, S1. The head is in the so-called active configuration with its light chain domain LCD tilted by 50° axially toward the M-line compared to rigor conformation (17), Z-line toward the bottom of the figure. Nonstereospecifically attached myosin heads can bind actin at various angles in the planes perpendicular (azimuthal plane) and parallel (axial plane) to the filament axis. Axial and azimuthal attachment angles of these heads are assumed to be uniformly distributed within ranges ±Ψax and ±Ψaz, respectively. (Inset) hexagonal unit cell in the projection perpendicular to the filament axis. Actin filaments are shown as small circles, all in the same orientation. The orientation of the myosin filaments is indicated by the positions of the origins of the myosin heads (short thick lines).