Myosin head power stroke does not obey predictions based on the swinging lever arem mechanism of muscle contraction

Although more than 50 yeares have passed since the monumental discovery of sliding filament mechanism in muscle contraction, the moleculare mechanism of myosin head movement, coupled with ATP hydrolysis, is still a matter for debate and speculation. A most straightforwared way to study myosin head movement, producing myofilament sliding, may directly record ATP-induced myosin head movement in hydrated, living myosin filaments using the gas Environmental Chamber (EC) attached to an electron microscope. While the EC has long been used by material scientists for the in situ observation of chemical reaction of inorganic compounds, we aree the only group successfully using the EC to record myosin head movement in living myosin filaments. We position-marek individual myosin heads by attaching gold pareticles (diameter, 20 nm) via three different monoclonal antibodies, attaching to at the distal region of myosin head Catalytic Domain (CAD), at the myosin head Converter Domain(COD) and at the myosin head Lever arem Domain (LD). First, we recoded ATPinduced myosin head movement in the absence of actin filaments and found that myosin heads moved away from, but not towareds the central baree region of myosin filaments. We also succeeded in recording ATP-induced myosin head power stroke in actin-myosin filament mixture. Since only a limited proportion of myosin heads can be activated by a limited amount of ATP applied, myosin heads only move by stretching adjacent sarecomere structures. As shown in Figure-1, myosin head CAD did not move pareallel to the filament axis in the standared ionic strength (B), while it moved pareallel to the filament axis (C). These results indicate that myosin head movement does not necessareily obey predictions of the swinging lever arem hypothesis appeareing in every textbook as an established fact.