myosin

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myosin

(mī`əsĭn), one of the two major proteinprotein,
any of the group of highly complex organic compounds found in all living cells and comprising the most abundant class of all biological molecules. Protein comprises approximately 50% of cellular dry weight.
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 constituents responsible for contraction of muscle. In muscle cells myosin is arranged in long filaments called thick filaments that lie parallel to the microfilaments of actinactin,
a protein abundantly present in many cells, especially muscle cells, that significantly contributes to the cell's structure and motility. Actin can very quickly assemble into long polymer rods called microfilaments.
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. In muscle contraction, filaments of actin alternately chemically link and unlink with those of myosin in a creeping or sliding action. The energy for this reaction is supplied by adenosine triphosphateadenosine triphosphate
(ATP) , organic compound composed of adenine, the sugar ribose, and three phosphate groups. ATP serves as the major energy source within the cell to drive a number of biological processes such as photosynthesis, muscle contraction, and the synthesis of
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. Myosin and actin also function in the motility of diverse non-muscle cells. In slime moldsslime mold
or slime fungus,
a heterotrophic organism once regarded as a fungus but later classified with the Protista. In a recent system of classification based on analysis of nucleic acid (genetic material) sequences, slime molds have been classified in a major group
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, for example, although present in much smaller quantities and forming shorter filaments, the interaction of the two proteins is employed to change cell shape and permit some movements.
The Columbia Electronic Encyclopedia™ Copyright © 2013, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Myosin

 

a fibrillar protein, a basic component of contractile muscle fibers (myofibrils); it constitutes 40–60 percent of the total muscle protein content. Myosin combines with another myofibrillar protein, actin, to form actomyosin, a primary structural element in the contractile muscular system. Another important property of myosin is its ability to split adenosine triphosphate (ATP) (V. A. Engel’gardt and M. N. Liubimova, 1939). Owing to the ATP-ase activity of myosin, the chemical energy of the high-energy ATP bonds is transformed into the mechanical energy necessary for muscular contraction. Myosin has a molecular weight of approximately 500,000. When acted upon by proteolytic enzymes, myosin decomposes into heavy meromyosin and light meromyosin (approximate molecular weights, 350,000 and 150,000, respectively).

Electron photomicrographs of myosin molecules reveal a bacilliform structure (1,600 × 25 angstroms), with two globular formations at one end. It is conjectured that the two polypeptide chains which make up the myosin molecule are twisted into a spiral. Proteins that are similar to myosin have been discovered in flagella, cilia, and other motile structures in many species of protozoa and bacteria, as well as in the spermatozoids of animals and certain plants.

REFERENCES

Poglazov, B. F. Struktura i funktsii sokratitel’nykh belkov. Moscow, 1965.
Finean, J R Rialagicheskie ul’$$$ Moacow, 1970. (Translated from English.)

V. O. SHPIKITER

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

myosin

[′mī·ə·sən]
(biochemistry)
A muscle protein, comprising up to 50% of the total muscle proteins; combines with actin to form actomycin.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
[20.] Haddad F, Jiang W, Bodell PW, Qin AX, Baldwin KM (2010) Cardiac myosin heavy chain gene regulation thyroid hormone involves altered histone modifications.
(2011) Muscle fiber type characterization and myosin heavy chain (MyHC) isoform expression in Mediterranean buffaloes.
After 10 days, the extract-treated cells were able to express a-actinin and myosin heavy chain, but not the other markers.
Myosin is a hexameric protein that consists of two myosin heavy chains and two pairs of non-identical light chains, the regulatory (RLC) and essential (ELC) light chains (15, 7).
Ueda et al., "Redifferentiation of smooth muscle cells after coronary angioplasty determined via myosin heavy chain expression," Circulation, vol.
This phosphorylated state accelerates progression of the myosin heavy chains along the actin filaments, since aggregation velocity increases significantly.
The myosin/actin (M/ A) and myosin/paramyosin (M/PM) ratios were calculated by dividing the areas of the myosin heavy chain (MHC) plus light chains by the actin and PM areas, respectively (Paredi et al.
A protein called myosin heavy chain controls muscle contractions in the heart.
(2000) proposed that endurance training in horses induces structural changes in the expression of isoforms of myosin heavy chain (MHC), involving transformations of MHCs of fast twitch to MHCs of slow twitch and that these changes depend on the duration and increase in activity, which are then reversed 3 months after the end of training.