Actin

Literature References: One of the major proteins of muscle and an important component of all eukaryotic cells. Formerly believed to be a single, highly conserved protein in all cell types, but multiple forms have been shown to exist. Muscle actin, or a-actin, is found in differentiated muscle cells; b-actin and g-actin are present in all non-muscle cell types. All three forms contain equimolar amounts of N-methylhistidine, although a-actin differs from b- and g-actins by several peptides; the two "non-muscle" actins are nearly identical. Several "minor actins" are also known. The various forms, although similar in activity, mol wt and amino acid composition, show immunological differences and are considered to be synthesized under the control of different genes. In addition to its role in muscle relaxation and contraction (together with myosin, q.v.), actin is involved in a variety of cellular events: cell movement, cytokinesis, phagocytosis, exocytosis and chromosome movement. Identification in muscle: F. B. Straub, Stud. Szeged 2, 3 (1942). Isoln: Feuer et al., Hung. Acta Physiol. 1, 150 (1948). Separation of actin from muscle material: A. Szent-Gyorgyi, US 2742456 (1956 to Armour). In soln, actin and myosin combine to give actomyosin: Tonomura et al., J. Biol. Chem. 237, 1074 (1962). Actin, in the absence of salts, exists in a globular form, designated as G-actin; in the presence of ATP and potassium, sodium, or magnesium chlorides it polymerizes to a fibrous form, F-actin. Removal of bound ATP results in complete loss of polymerizability: Straub, Feuer, Biochim. Biophys. Acta 4, 455 (1950). Structure of G-actin: Nagy, Jencks, Biochemistry 1, 987 (1962); of F-actin: Hanson, Lowy, J. Mol. Biol. 6, 46 (1963). Complete amino acid sequence of rabbit skeletal muscle actin: Elzinga et al., Proc. Natl. Acad. Sci. USA 70, 2687 (1973). Identification and characterization of multiple forms of actin: J. I. Garrels, W. Gibson, Cell 9, 793 (1976). Partial amino acid sequence of calf brain actin: R. C. Lu, M. Elzinga, Biochemistry 16, 5801 (1977). Comparison of actins from calf thymus, bovine brain, mouse cells and rabbit skeletal muscle: J. Vandeker, K. Weber, Eur. J. Biochem. 90, 451 (1978). Isoln, characterization of porcine brain actin: J. P. Weir, D. W. Frederik, Arch. Biochem. 203, 1 (1980). In vivo and in vitro synthesis of multiple forms of rat brain actin: E. Palmer, J. L. Saborio, J. Biol. Chem. 253, 7482 (1978). Evidence for control of synthesis of human heart and platelet actins by different genes: M. Elzinga et al., Science 191, 94 (1976). Immunological differences between cardiac muscle, skeletal muscle and brain actins: J. L. Morgan et al., Proc. Natl. Acad. Sci. USA 77, 2069 (1980). History of discovery: Finck, Science 160, 332 (1968). Reviews: Several authors, Biochemistry of Muscle Contraction, J. Gergely, Ed. (Little, Brown, Boston, 1964); Laki, "Actin" in Contractile Proteins and Muscle, K. Laki, Ed. (Marcel Dekker, New York, 1971) pp 97-133; E. D. Korn, Proc. Natl. Acad. Sci. USA 75, 588-599 (1978); R. Kassab et al., Biochimie 63, 273-289 (1981); S. Highsmith, Biochim. Biophys. Acta 639, 31-39 (1981); E. D. Korn, Physiol. Rev. 62, 672-737 (1982).