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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. 2015.
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Examples from the web for actin
  • One that churns out actin and myosin, which link up to form units that can expand and contract, will become a muscle cell.
  • Nucleated cells have an internal scaffolding called a cytoskeleton, made in part of filaments of the protein actin.
  • Myosin is a small globular proteins with two little feet that move in discrete steps along long chains of actin.
  • These little guys crawl rather than swim, and the amazing thing is they have no actin.
  • Normally the actin bounces along the myosin molecules, dragging the magnets and generating a tiny current.
  • Myosin is the molecular motor of muscle contraction: when it receives a particular chemical signal, it tugs on actin.
  • One of them causes a host protein called actin to clump together into long filaments.
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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