Bi‐directional movement of actin filaments along long bipolar tracks of oriented rabbit skeletal muscle myosin molecules

In actomyosin in vitro motility assays, orientation of myosin molecules affects their interaction with actin. We obtained long tracks of myosin molecules with uniform orientation. Bipolar filaments about 50 microm long were made from myosin rod prepared from molluscan smooth muscles, to which rabbit skeletal-muscle myosin bound, creating long synthetic thick-filaments. Movement of F-actin toward their center was much faster (4.7 +/- 0.6 microm s(-1)) than in the opposite direction (1.9 +/- 0.2 microm s(-1)), indicating that myosin molecules were arranged in the same orientation along each half of the bipolar filament. These complex thick-filaments permit measurement of actin movement over 20 microm of oriented skeletal myosin tracks facilitating mechanistic studies of actomyosin motility.