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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

See Examples For:

actin actin-

Further investigation showed that this dark band represented a wave of soluble actin, a key protein involved in cell movement, being rapidly pushed forward.

From Science Daily ● Apr. 1, 2026

During interphase, these asters help determine where the actin band will form, marking the future division site.

From Science Daily ● Feb. 28, 2026

In both cases, the actin band collapsed without microtubules, demonstrating that these structures provide crucial mechanical support and signaling during band formation and contraction.

From Science Daily ● Feb. 28, 2026

To confirm that the observed differences were truly caused by the actin mutation and not by other genetic variations, the researchers performed a crucial control experiment.

From Science Daily ● Dec. 17, 2025

“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

Myosin heads will not detach from the actin- binding sites, resulting in muscle stiffness.

From Textbooks ● Jun. 9, 2022

Myosin heads will detach rapidly from the actin- binding sites, resulting in muscle relaxation.

From Textbooks ● Jun. 9, 2022

The Ca++ ions in the sarcoplasm have bound to troponin, tropomyosin has shifted away from actin- binding sites, cross-bridges formed, and sarcomeres are actively shortening to the point of peak tension.

From Textbooks ● Jun. 19, 2013