actin

n. globulin which is found in muscle plasma and aids in muscle contraction (Biochemistry)

Actin is a globular structural, 42-47 kDa protein found in many eukaryotic cells, with concentrations of over 100 μM. It is also one of the most highly conserved proteins, differing by no more than 5% in species as diverse as algae and humans. It is the monomeric subunit of microfilaments, one of the three major components of the cytoskeleton, and of thin filaments which are part of the contractile apparatus in muscle cells. Thus, actin participates in many important cellular functions, including muscle contraction, cell motility, cell division and cytokinesis, vesicle and organelle movement, cell signaling, and the establishment and maintenance of cell junctions and cell shape.
See more at Wikipedia.org...

Actin /ac·tin/ a muscle protein localized in the I band of the myofibrils; acting along with myosin, it is responsible for contraction and [more]Actin - Community and Resources

Noun
1. one of the proteins into which actomyosin can be split; can exist in either a globular or a fibrous form
(hypernym) simple protein
(substance-holonym) actomyosin

v. open, elaborate, open up, uncover, unclose, unwrap, clear away, clear, clear up, expand, open out, spread out, unfold, unfurl, untie, undo, unbind, unlock, turn on, switch on, ring up, disclose, sharpen, whet, bring up in conversation