Motion of myosin filaments due to interaction of the two-headed myosin crossbridge with two actin filaments.

A model of a two-headed myosin crossbridge, whose motion is realized by alternate stepping of its two heads on two actin filaments, is proposed. The geometrical possibility of such crossbridge stepping in contracting skeletal muscle is shown, provided that a free myosin head can bind to an actin filament at a right angle and the attached one can tilt to a greater angle than 45 degrees. Motion of a myosin-like protein along actin filaments in Characean alga cells can proceed by a similar mechanism.