Electron microscopic recording of myosin head power stroke in hydrated myosin filaments.
Muscle contraction results from cyclic attachment and detachment between myosin heads and actin filaments, coupled with ATP hydrolysis. Despite extensive studies, however, the amplitude of myosin head power stroke still remains to be a mystery. Using the gas environmental chamber, we have succeeded in recording the power stroke of position-marked myosin heads in hydrated mixture of actin and myosin filaments in a nearly isometric condition, in which myosin heads do not produce gross myofilament sliding, but only stretch adjacent elastic structures. On application of ATP, individual myosin heads move by ~3.3 nm at the distal region, and by ~2.5 nm at the proximal region of myosin head catalytic domain. After exhaustion of applied ATP, individual myosin heads return towards their initial position. At low ionic strength, the amplitude of myosin head power stroke increases to >4 nm at both distal and proximal regions of myosin heads catalytic domain, being consistent with the report that the force generated by individual myosin heads in muscle fibers is enhanced at low ionic strength. The advantages of the present study over other in vitro motility assay systems, using myosin heads detached from myosin filaments, are discussed.
Department of Physiology, School of Medicine, Teikyo University, Itabashi-ku, Tokyo 173-8605, Japan.
Haruo
H
Sugi
Department of Integrated Sciences in Physics and Biology, College of Humanities and Sciences, Nihon University, Setagaya-ku, Tokyo 156-8550, Japan.
Shigeru
S
Chaen
Department of Physiology, School of Medicine, Teikyo University, Itabashi-ku, Tokyo 173-8605, Japan.
Tsuyoshi
T
Akimoto
Department of Applied Physics, Tokyo University of Agriculture and Technology, Koganei-shi, Tokyo 184-8588, Japan.
Hiroki
H
Minoda
Graduate School of Agricultural and Life Sciences, University of Tokyo, Bunkyo-ku, Tokyo 113-0032, Japan.
Takuya
T
Miyakawa
Graduate School of Agricultural and Life Sciences, University of Tokyo, Bunkyo-ku, Tokyo 113-0032, Japan.
Yumiko
Y
Miyauchi
Graduate School of Agricultural and Life Sciences, University of Tokyo, Bunkyo-ku, Tokyo 113-0032, Japan.
Masaru
M
Tanokura
Graduate School of Frontier Sciences, University of Tokyo, Kashiwa-shi, Chiba 277-8563, Japan.
Seiryo
S
Sugiura
D008841:Actin Cytoskeleton / Q000737:chemistry* / Q000378:metabolism*; D000199:Actins / Q000737:chemistry / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D020134:Catalytic Domain; D008297:Male; D008854:Microscopy, Electron; D009119:Muscle Contraction / Q000502:physiology; D009218:Myosins / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure*; D009994:Osmolar Concentration; D011817:Rabbits
D000199:Actins; D000255:Adenosine Triphosphate; D009218:Myosins