| Budget Amount *help |
¥5,500,000 (Direct Cost: ¥5,500,000)
Fiscal Year 1989: ¥1,600,000 (Direct Cost: ¥1,600,000)
Fiscal Year 1988: ¥3,900,000 (Direct Cost: ¥3,900,000)
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| Research Abstract |
I attempted to observe the structure of muscle cross-bridges or myosin heads while sliding along thin filaments, with high special and temporal resolution obtained by quick-freezing electron microscopy, since any structural change accompanied with the sliding could be crucial to elucidate the molecular mechanism of "sliding movement". The study was started with the simplest system; a mixture of purified myosin subfragment-1 (S1) and F-actin as test specimen, to avoid the difficulty which arises from using whole muscle fiber; i.e.) the structural change in each head cannot be homogenous because of the restriction not only by two connected heads in a single molecule, but also by forming thick filaments. Using improved mica-flake technique coupled with quick-freeze deep-etch method, I presented the evidences, for the first time, indicating that S1 molecules appear elongated and attached to actin in a tilted manner under rigor condition or in the presence of ADP, whereas they are short and rounded if ADP.Vi or ATP is incorporated. Subsequent observation of heavy meromyosin molecules; each having two heads but does not form filament; in the presence of various nucleotides made it clear that the observed rounding of S1 would have come from the flection in myosin head. Though the presence of such large conformational change in myosin head has never been observed by electron microscopy, accumulating evidences from recent biochemical studies are quite compatible with this observation. Myosin heads seen in actomysin specimen during superprecipitation; the putative in vitro model system corresponding to muscle contraction; showed a similar morphological feature, suggesting the possibility that such conformational change actually occurring in actively contracting muscle.
Several new findings were also obtained concerning the functional domain organization and the conformation in solution, of caldesmon; the putative regulatory protein involved in smooth muscle contraction.
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