Takayuki Nishizaka

F₁-ATPase is a rotary molecular motor in which unidirectional rotation of the central <symbol>γ</symbol>-subunit is powered by ATP hydrolysis in three catalytic sites arranged 120° apart around <symbol>γ</symbol>. To see how hydrolysis reactions produce mechanical rotation, we observed rotation of <symbol>γ</symbol> under the optical microscope, while watching which of the three sites bound and released a fluorescent ATP analog. The reaction scheme, including both the number of site occupancy and reactions that trigger substeps, is now established.<br>

We sumrnarize the mechanical and functional properties of a motormolecule of muscle studied with a new type of an in vitro motility assay system and a multi-imaging microscope system. First, supercoiling of an actin filament is shown, suggesting that the filament moves forward like a right-handed screw. Second, we describe the unbinding force and the lifetime of a rigor bond between a single myosin molecule and an actin filament measured by using optical tweezers. From these results, the mechanism of sliding and force generation of the motor molecule is discussed.