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It is generally accepted that muscle contraction is the result of cyclic interaction of parts of the myosin molecules (the myosin heads, or the “cross-bridges”) with the actin filaments (A.F. Huxley, 1957, 1974; Pringle, 1967; H.E.Huxley, 1969). According to recent biochemical studies (Stein et al., 1979; Rosenfeld and Taylor, 1984; Hibberd and Trentham, 1986) and mechanical and X-ray diffraction experiments on skinned fibers (Brenner et al., 1982, 1984, 1986; Yu and Brenner, 1989), cross-bridges exist in two main configurations, a configuration with low actin affinity (weak cross-bridge binding) and a configuration with high actin affinity (strong cross-bridge binding). During ATP-hydrolysis, cross-bridges are thought to cycle between these two main configurations (Eisenberg and Greene, 1980; Eisenberg and Hill, 1985). Furthermore, it was proposed that force is generated when the attached cross-bridge changes its configuration from the weak- to the strong-binding form (Eisenberg and Hill, 1985). |
