FORCE-VELOCITY RELATION OF SLIDING OF SKELETAL-MUSCLE MYOSIN, ARRANGED ON A PARAMYOSIN FILAMENT, ON ACTIN CABLES

To investigate in vitro ATP-dependent sliding of regularly arranged my osin molecules on actin filaments, we prepared thick hybrid filaments in which myosin molecules isolated from rabbit skeletal muscle were ar ranged around the paramyosin core (length, 10-20 mu m; diameter, less than or equal to 0.21 mu m) obtained from a molluscan smooth muscle, A single to a few thick hybrid filaments were attached to a polystyrene bead (diameter, 4.5 mu m; specific gravity, 1.5) and made to slide on actin filament arrays (actin cables) in the internodal cell of an alg a, mounted on the rotor of a centrifuge microscope. The bead was subje cted to centrifugal forces serving as external loads to the ATP-depend ent actin-myosin sliding. The maximum unloaded sliding velocity of the thick filament attached-bead (mean, 3.4 mu m/s; 20-23 degrees C) was significantly higher than that of the bead coated with randomly orient ed myosin molecules reported previously. The steady-state force-veloci ty (P-V) relations obtained were qualitatively similar to those in int act skeletal muscle fibers. These results indicate that this in vitro motility assay system retains the basic characteristics of contracting skeletal muscle fibers, and that it may be effectively used to study mechanisms underlying the steady-state P-V characteristics of ATP-depe ndent actin-myosin sliding using various recombinant myosins produced in nonmuscle cells.