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(Science: cell biology) a filamentous proteins (42 kD) involved in muscle contraction in both smooth and striated muscle and also serves as an important structural molecule for the cytoskeleton of many eukaryotic cells.
It is the main constituent of the thin filaments of muscle fibres. The filaments (known also as filamentous or f-actin) can be dissociated into their globular subunits; each subunit is composed of a single polypeptide 375 amino acids long. this is known as globular or g-actin. in conjunction with myosin, actin is responsible for the contraction and relaxation of muscle.
See: myosin.
One of the proteins into which actomyosin can be split; can exist in either a globular or a fibrous form.A protein found in the muscles of organisms that is initiated by atp to allow contraction of a muscle.

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