Displacements of single one-headed myosin molecules in a sparse myosin- rod cofilament were measured from bead displacements at various angles relative to an actin filament by dual optical trapping nanometry. The sparse myosin-rod cofilaments, 5-8 μm long, were synthesized by slowly mixing one- headed myosin prepared by papain digestion with myosin rods at molar ratios of 1:400 to 1:1500, so that one to four one-headed myosin molecules were on average scattered along the cofilament. The bead displacement was ~10 nm at low loads (~0.5 pN) and at angles of 5-10°between the actin and myosin filaments (near physiologically correct orientation). The bead displacement decreased with an increase in the angle. The bead displacement at nearly 90°was ~0 nm. When the angle was increased to ~150°-170°, the bead displacements increased to 5 nm. A native two-headed myosin showed similar size and orientation dependence of bead displacements as a one-headed myosin.
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