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• actin
  actin

  noun

  a globulin that is present in muscle plasma and that in connection with myosin plays an important role in muscle contraction.
• actin-
  actin-

  variant of actino- before a vowel.

actin

¹ American  

[ak-tuhn] / ˈæk tən /

noun

Biochemistry.

1. a globulin that is present in muscle plasma and that in connection with myosin plays an important role in muscle contraction.

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actin- ² American  

1. variant of actino- before a vowel.

   actinism.

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actin British  

/ ˈæktɪn /

noun

1. a protein that participates in many kinds of cell movement, including muscle contraction, during which it interacts with filaments of a second protein, myosin

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actin Scientific  

/ ăk′tĭn /

1. A protein found in all eukaryotic cells, forming filaments that make up a main component of the cell's supporting matrix or cytoskeleton. Actin and the protein myosin together make up the contractile units (called sarcomeres) of skeletal muscle fibers.

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Etymology

Origin of actin

1940–45; perhaps act + -in ²

Example Sentences

Because microtubules can influence how stiff the cytoplasm is, the researchers asked whether asters might help anchor the actin band by stiffening the cell interior.

From Science Daily • Feb. 28, 2026

In these cases, the sheer size of the cell and the presence of a large yolk sac prevent the actin ring from fully closing.

From Science Daily • Feb. 28, 2026

They discovered that the cytoplasm becomes stiffer during interphase, creating a supportive scaffold that stabilizes the actin band.

From Science Daily • Feb. 28, 2026

In many organisms, cells divide by building a ring made of the protein actin at the cell's midpoint.

From Science Daily • Feb. 28, 2026

“You don’t understand. Him and State ain’t actin like they just hidin him. They actin like he did it.”

From "Song of Solomon" by Toni Morrison