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[ak-tuh n] /ˈæk tən/
noun, Biochemistry.
a globulin that is present in muscle plasma and that in connection with myosin plays an important role in muscle contraction.
Origin of actin
1940-45; perhaps act + -in2


variant of actino- before a vowel:
actinism. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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Examples from the Web for actin
Historical Examples
  • "The mare's actin' as if she'd a cup of tea, too," muttered her companion, Ned.

    Thoroughbreds W. A. Fraser
  • And yet, if she wanted Jonadab, she was actin' mighty funny.

    The Depot Master Joseph C. Lincoln
  • The nigher we got, the harder he stared; and the man in front was actin' similar in regards to him.

    The Depot Master Joseph C. Lincoln
  • All I should be able to think of was what she wore, or didn't wear, when she was actin' her parts.

    Kent Knowles: Quahaug Joseph C. Lincoln
  • Your Uncle Zoeth and me have been actin' as your pilots for a consider'ble spell.

    Mary-'Gusta Joseph C. Lincoln
  • I'm plum 'shamed of the way our gals is actin' with the boarders.

    Janet of the Dunes

    Harriet T. Comstock
  • That's what my boys was brought up to think, 'n they're actin' accordin'.

    Peak and Prairie Anna Fuller
  • "Oi don't loike th' way he is actin', Frankie," whispered Barney.

    Frank Merriwell's Bravery Burt L. Standish
  • Master Langdon 's actin' under my orders, and I claim that hoss and all that's on him.

    Elsie Venner Oliver Wendell Holmes, Sr.
  • You're actin' square by my poor gal, sir, so I'm agoin' to act square by you.

    The Bishop's Secret

    Fergus Hume
British Dictionary definitions for actin


a protein that participates in many kinds of cell movement, including muscle contraction, during which it interacts with filaments of a second protein, myosin
Word Origin
C20: from act + -in
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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actin in Medicine

actin ac·tin (āk'tĭn)
One of the protein components found in muscle, existing as F-actin or G-actin, into which actomyosin can be split and which acts with myosin in muscle contraction.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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actin in Science
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.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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