- A globulin present in muscle that has an ATPase activity; in combination with actin, it forms actomyosin; m. forms the thick filaments in muscle.- m. light chain kinase a calcium/calmodulin-dependent enzyme that phosphorylates the light chains of smooth muscle m. and initiates contraction. In skeletal muscle, phosphorylation modulates tension during contraction.
* * *my·o·sin 'mī-ə-sən n1) ACTOMYOSIN2) a fibrous globulin of muscle that can split ATP and that reacts with actin to form actomyosin
* * *n.the most abundant protein in muscle fibrils, having the important properties of elasticity and contractility. With actin, it comprises the principal contractile element of muscles. See striated muscle.
* * *my·o·sin (miґo-sin) any of a family of proteins with ATPase activity, existing in a number of isoforms; it moves along actin filaments (F-actin) using the energy from ATP hydrolysis. Myosin consists of a head that produces motion by â€œwalkingâ€ along the actin filament and is joined by a neck domain to a tail that contains binding sites determining specific activity. Within cells, myosins are involved in transport of vesicles and organelles. Myosin II, made up of two heavy and four light chains, is the main constituent of the thick filaments of muscle fibers, is responsible for the contraction and relaxation of muscle, and is the motor that drives cytokinesis. Cf. actomyosin. See Plate 32.
Medical dictionary. 2011.