Troponin Subunits and Their Interactions

The activation of muscle contraction is believed to be mediated by the interaction of calcium with troponin in the myofibril (Ebashi et al., 1967; Fuchs and Briggs, 1968). To understand this interaction, the location of the calcium binding sites on troponin and the intra- and intermolecular changes which accompany the Ca++ binding and release must be determined. Toward this end we have separated the protein components that are usually present in troponin preparations and studied their properties. The purpose of this report is to describe some of the characteristics of the individual troponin subunits and the protein-protein interactions which occur both among themselves and with tropomyosin.