Tropomyosins

Literature References: Fibrous proteins involved in the regulation of muscle relaxation. They are present in all forms of striated and smooth muscles and probably in nonmuscle cells as well. Native tropomyosin consisting of two proteins, tropomyosin and troponin, is the Ca2+-sensitive regulatory protein that controls the interaction between actin and myosin necessary for the production of force in muscle. In all skeletal tissues, there are two forms of tropomyosin chains, designated a and b. Their ratio depends on the muscle source. Troponin consists of three subunits, troponin T (the tropomyosin binding subunit), troponin I (the actomyosin ATPase inhibitory subunit) and troponin C (the Ca2+-binding subunit). All three subunits, in addition to tropomyosin, are responsible for the native tropomyosin activity. Isoln of tropomyosin from skeletal muscle and cardiac muscle: K. Bailey, Nature 157, 368 (1946); idem, Biochem. J. 43, 271 (1948). Structure studies: R. S. Hodges, L. B. Smillie, Biochem. Biophys. Res. Commun. 41, 987 (1970). Amino acid sequence studies: J. Sodek et al., Proc. Natl. Acad. Sci. USA 69, 3800 (1972). X-ray crystal structure of troponin C: M. Sundaralingam et al., Science 227, 945 (1985). Reviews: C. E. Bodwell, K. Laki, in Contractile Proteins and Muscle, K. Laki, Ed. (Dekker, New York, 1971); W. F. Harrington in The Proteins vol. 4, H. Neurath, R. L. Hill, Eds. (Academic Press, New York, 1979) pp 317-327. Comprehensive review of isolation, preparation, identification and role in the contractile process: "Structural and Contractile Proteins" in Methods Enzymol. 85, Part B, 1-774 (1982).