The Mechanism of Muscle Contractio

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Knowledge of the mechanism of contraction has been obtained from studies of the interaction of and in solution, from an elucidation of the structure of muscle fibers, and from measurements of the mechanics and energetics of fiber contraction. Many of the states and the transition rates between them have been established for the hydrolysis of ATP by and subfragments in solution. A major goal is to now understand how the kinetics of this interaction are altered when it occurs in the organized array of the . Early work on the structure of muscle suggested that changes in the orientation of cross-bridges were responsible for the generation of force. More recently, fluorescent and paramagnetic probes attached to the cross-bridges have suggested that at least some domains of the cross-bridges do not change orientation during force generation. A number of properties of active cross-bridges have been defined by measurements of steady state contractions of fibers and by the transients which follow step changes in fiber length or tension. Taken together these studies have provided firm evidence that force is generated by a cyclic interaction in which a cross-bridge attaches to , exerts force through a "powerstroke" of 12 nm, and is then released by the of ATP. The mechanism of this interaction at the molecular level remains unknown.

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Animals Humans Muscles Myosins Nucleotides Actomyosin Myosin Subfragments Tropomyosin Protein Conformation Flight, Animal