The main focus of this research will be to: Extend the refinement studies on CaTNC from chicken skeletal muscle from 2.0 alpha to 1.7 alpha resolution; complete the refinement of the isomorphous MnTNC structure at 2.2 alpha resolution; extend the data of Cd and NdTNC to higher resolution for refinement; prepare MgTNC and the four-calcium state TNC for crystallization and x-ray structure analysis; seek optimum conditions to improve the quality and size of the initial crystals that we have obtained on bovine cardiac TNC (which binds only three calcium ions) for possible x-ray structure determination; carry out crystallization of the multiprotein complexes the whole troponin C + I + T, and C + I. Besides the crystallographic work, quantitative structure-activity relationship studies (QSAR) will be conducted relating binding constants, ligand charge, hydrophobicity of helices and beta-sheets; in addition, the role of charged side chains on the stability of alpha-helices exposed to solvent will continue to.be investigated. We have made important advances in many of these studies. The x-ray and QSAR studies are providing a wealth of information on the structural principles governing the calcium-binding proteins and the nature of the forces controlling the calcium binding affinities. The high resolution structural information on the troponin family of muscle proteins will help towards a better understanding of the molecular mechanism of muscular contraction and thus provide insights on various disease states.