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Calcium sensitive binding of troponin to actin-tropomyosin: A two-site model for troponin action

1973; Elsevier BV; Volume: 80; Issue: 4 Linguagem: Inglês

10.1016/0022-2836(73)90212-x

1089-8638

Sarah E. Hitchcock, H. E. Huxley, Andrew G. Szent‐Györgyi,

Metal and Thin Film Mechanics

Troponin reconstituted from the inhibitory component (troponin-I) and calcium binding protein (troponin-C) binds readily to actin-tropomyosin in 0.1 mm-EGTA but only poorly in 0.01 mm-CaCl2 or 0.1 mm-Ca-EGTA. Troponin prepared by extraction of myofibrils with mersalyl, an organic mercurial, contains only these two components and also shows this calcium-sensitive binding and is deficient in its ability to bind to tropomyosin. Troponin-I + C is unable to confer calcium sensitivity on the Mg2+ activated actomyosin ATPase in concentrations at which native troponin is fully effective and the ATPase activity remains high in the absence of calcium. Addition of the tropomyosin binding component (troponin-T) to the other two components restores their ability to remain associated with actin-tropomyosin in the presence of calcium as does native troponin; calcium sensitivity is also regained. The results of these experiments have been interpreted in terms of a two-site mechanism of troponin action.