actin

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actin A contractile protein found in muscle tissue, in which it occurs in the form of filaments (called thin filaments). Each thin filament consists of two chains of globular actin molecules, around which is twisted a strand of tropomyosin and interspersed troponin. Units of muscle fibre (see sarcomere) consist of actin and myosin filaments, which interact to bring about muscle contraction (see also sliding filament theory). Actin is also found in the microfilaments that form part of the cytoskeleton of all cells.

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actin, a protein abundantly present in many cells, especially muscle cells, that significantly contributes to the cell's structure and motility. Actin can very quickly assemble into long polymer rods called microfilaments. These microfilaments have a variety of roles—they form part of the cell's cytoskeleton, they interact with myosin to permit movement of the cell, and they pinch the cell into two during cell division. In muscle contraction, filaments of actin and myosin alternately unlink and chemically link in a sliding action. The energy for this reaction is supplied by adenosine triphosphate.

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actin A globular protein of relative molecular mass 60 000 which is a major component of microfilaments generally, and which is especially important in the myofibrils of striated muscle cell.

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actin (ak-tin) n. a protein, found in muscle, that plays an important role in the process of contraction. See striated muscle.