1987 年 27 巻 4 号 p. a165-a171
Recently, evidence has been accumulating that the actual molecular mechanism of muscle contraction may be completely different from the widely accepted contraction models by A.F. Huxley (1957) and Huxley and Simmons (1971). Recent experimental results are presented and discussed on the following six topics, i.e., (1) time-resolved X-ray diffraction studies on contracting muscle by use of synchrotron radiation, (2) electron microscopic observation of structural changes of the cross-bridges, (3) weak and strong binding states between the cross-bridges and the thin filaments, (4) distance of a power stroke of the cross-bridges, (5) cooperative interaction of myosin two heads in muscle contraction, and (6) model experiments on muscle contraction by use of the actin cable in plant cells.
It is concluded that (1) active structural changes take place in actin molecules in the thin filaments during activation of contraction, (2) the cross-bridges may well keep their 143A periodicity during contraction, (3) the distance over which a cross-bridge can slide the thin filament by the splitting of one ATP molecule may be much larger than that expected from a simple cross-bridge power stroke, and (4) cooperative interactions between the two heads of myosin is necessary for producing force and motion in muscle fibers, though in more simplified systems single-headed myosin can also produce force and motion.