Evidence for the essential role of myosin subfragment-2 in the ATP-dependent actin-myosin sliding in muscle contraction.
The role of myosin subfragment-2 (myosin S-2) in muscle contraction was studied by using an in vitro motility assay system in which the ATP-dependent sliding between myosin-coated polystyrene beads and actin filament arrays (actin cables) of giant algal cells were recorded under constant external loads provided with a centrifuge microscope. With antibody to myosin S-2 below 0.3 mg/ml, the maximum "isometric" force generated by myosin molecules on the bead decreased markedly, but the unloaded bead-sliding velocity along actin cables did not change appreciably, indicating a decrease in the number of myosin molecules interacting with actin cables. The antibody at 0.3-1.5 mg/ml decreased not only the maximum isometric force, but also the unloaded bead-sliding velocity in a dose-dependent manner. With the antibody at 1.5-3 mg/ml, the beads eventually stopped moving to remain attached to actin cables. These beads could be readily detached from actin cables with very small centrifugal forces, indicating very weak actin-myosin linkages. The antibody had no effect on rigor actin-myosin linkages formed before the antibody application. These results are consistent with the view that myosin S-2 plays an essential role in muscle contraction.
Tsuchiya
T
T
Department of Biology, Faculty of Science, Kobe University, Nada-ku, Kobe, 657-0013, Japan.
Tanaka
H
H
Shirakawa
I
I
Karr
T
T
Sugi
H
H
D000199:Actins / Q000502:physiology*; D000255:Adenosine Triphosphate / Q000502:physiology*; D000818:Animals; D000906:Antibodies; D066298:In Vitro Techniques; D018715:Microscopy, Video; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology; D015879:Myosin Subfragments / Q000037:antagonists & inhibitors / Q000276:immunology / Q000502:physiology*; D009218:Myosins / Q000502:physiology; D011137:Polystyrenes; D011817:Rabbits
D000199:Actins; D000906:Antibodies; D015879:Myosin Subfragments; D011137:Polystyrenes; D000255:Adenosine Triphosphate; D009218:Myosins