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.

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

myosin

[′mī·ə·sən]
(biochemistry)
A muscle protein, comprising up to 50% of the total muscle proteins; combines with actin to form actomycin.
References in periodicals archive ?
Caption: Figure 4: Systemic mesenchymal stem cells (MSCs) administration prevents the decreased myosin heavy chain (MHC) levels in the tibialis anterior (TA) muscle of mice fed with a high fat diet (HFD).
Haddad F, Jiang W, Bodell PW, Qin AX, Baldwin KM (2010) Cardiac myosin heavy chain gene regulation thyroid hormone involves altered histone modifications.
After 10 days, the extract-treated cells were able to express a-actinin and myosin heavy chain, but not the other markers.
Analysis of myosin heavy chains at the protein level in horse skeletal muscle.
Two proteins differentially regulated in glioma cells were found using DIGE proteomics: pericentrin B and non muscle myosin heavy chain.
The level of muscle strength is strongly related to amount of myosin heavy chain (MHC) present in the body.
Nomarsky optics and immunohistochemical techniques with antibodies to the [alpha]2(IV) chain, myosin heavy chain, and GFP are being used to analyze the phenotypic defects exhibited by homozygous animals with a CBS mutation.
Western blot analysis revealed myogenic terminal proteins such as desmin and myosin heavy chain (MF20) in the differentiated rQM7 cells, but not in the differentiated MyoD KO QM7#4 cells (Figure 4D).