Literature References: Mol wt approx 500,000. The main protein in muscle, which, by hydrolyzing ATP, provides the energy necessary for muscular contraction. Individual molecules are rod-shaped and consist of two globular heads attached flexibly to a tail of approx 1500Å length. All muscle myosins have a similar subunit structure composed of two heavy chains and two distinct pairs of light chains. One of the light chains is involved in a Ca2+-dependent regulatory process in the vertebrate skeletal muscle system. Biological prepn and review: A. G. Szent-Györgyi, Chemistry of Muscular Contraction (Academic Press, New York, 2nd ed., 1951) pp 38-57, 146-148. Other reviews: idem, Adv. Enzymol. Relat. Subj. Biochem. 16, 313-360 (1955); A. G. Szent-Györgyi et al., in Sulfur in Proteins, R. Benesch et al., Eds. (Academic Press, New York, 1959) pp 291-295; J. Gergely, Biochemistry of Muscle Contraction (Little, Brown, Boston, 1964) pp 3-115; several authors in Contractile Proteins and Muscle, K. Laki, Ed. (Dekker, New York, 1971); several authors in Methods Enzymol. 85, Part B, 55-130 (1982). Review on structure and function of myosin: W. F. Harrington, "Contractile Proteins of Muscle" in The Proteins vol. 4, H. Neurath, R. L. Hill, Eds. (Academic Press, New York, 1979) p 245-409. Polymorphism of mammalian myosins and distribution of isoforms in different muscle fibers reviewed by A. G. Weeds in Plasticity of Muscle, D. Pette, Ed. (DeGruyter, Berlin, 1980) pp 55-68. Role of myosin light chains in calcium regulation: Kendrick-Jones, Nature 249, 631 (1974). Tertiary crystal structure of globular heads: I. Rayment et al., Science 261, 50 (1993). See also Tropomyosin.