MECHANOCHEMICAL COUPLING OF CROSS-BRIDGES

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The overall aims of this research are to understand the molecular mechanism by which muscle proteins convert chemical energy into mechanical work, and to obtain a precise correlation between the physiological and biochemical events of muscular contraction. Novel methods will be applied to striated muscle fibers to probe the relations between biochemical reactions of the contractile proteins, the elementary mechanical steps of the cross-bridge cycle and the corresponding structural motions. Rapid changes in the chemical concentrations of pertinent biochemical species, such as ATP, will be made by laser pulse photolysis of photolabile "caged" precursors. A newly developed method to secure the fiber ends will be used to improve the uniformity and reproducibility of the contractions.Rapid mechanical transients initiated by quick length changes will be obtained under conditions with altered concentrations of the biochemical substrate and products. Kinetics modelling, involving a novel method to determine theoretical values directly from the experiments, will be used to help interpret the results. The isotonic filament sliding distance per substrate molecule utilized by the contractile proteins will be determined to relate the number of enzymatic cycles to the number of mechanical interfilament interactions. Rapidly repeated steps of shortening after photo release of known and limited concentrations of substrate will provide a direct indication of the mechano-chemical coupling ratio. The experiments will be carried out on single muscle fibers of rabbit psoas and frog semitendinosus muscles that have had the surface membrane removed to allow alterations to the biochemical environment of the proteins. Results from this project should significantly advance knowledge of the contractile process and thus bring a greater understanding of both normal and pathological states of striated muscle and other types of cell motility.