The long-term objective of this project is to elucidate the mechanisms for 1) transduction of energy during contraction of skeletal muscle, 2) the regulation of skeletal muscle contraction by calcium ions. Since these two processes are fundamental to the functioning of normal muscle tissue, this work may provide insight into the nature of pathological muscle conditions. This objective will be achieved by determining the spatial relationships among the four major contractile proteins: myosin, actin, tropomyosin and troponin. Furthermore, how these spatial relationships change with the functional state of muscle (relaxed, activated, or in rigor) will be examined. Information so derived will be used to reconstruct the molecular events that occur during muscle contraction and its regulation. Principally, two techniques will be used to determine spatial relationships: excitation energy transfer, and photochemical crosslinking. The distances between sites in tropomyosin and in the three subunits of troponin will be determined by excitation energy transfer measurements. Simultaneously, amino acid residues at the interfaces between the proteins will be identified using photocrosslinking and peptide analysis techniques. Information derived from these studies will be used to construct a three-dimensional model for the troponin.tropomyosin complex. In a similar fashion, distances between sites in tropomyosin, actin and myosin will be determined, and the interaction interfaces between these proteins identified. This will yield information on the location of tropomyosin in the myosin.actin.tropomyosin complex, and the contact region between myosin and actin.