myosin

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Related to Myosins: Myosin Heavy Chain, myosin V

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 ?
These protein profiles are mainly comprised myosin and actin, and containing other proteins such as troponin, tropomyosin, a-actinin and c-protein which are mainly connected with myosin and actin [23].
Decreased myosin expression, as demonstrated by IHC staining, suggested that altered muscle protein conformation may have occurred, which is consistent with effects of methylmercury on muscle development in zebrafish embryos (Liu et al.).
She pointed out that the damage triggers a defense mechanism that quickly builds the actin filament while getting the myosin ready for further action.
Phosphorylation by ROCK inactivates a myosin phosphatase, retaining myosin II in the phosphorylated or active state [34, 35].
Myosin XVA, expressed at the tips of stereocilia in the cochlea hair cells, is essential for the function of mechanotransduction apparatus [13], which is proved by a myosin XVA-deficient mouse model study [14].
It has been reported that myosin is implicated in endothelial barrier signaling [56].
(1992) Control of nonmuscle myosins by phosphorylation.
Differences in two-dimensional gel electrophoresis patterns of skeletal muscle myosin light chain isoforms between Bos taurus, Sus scrofa and selected poultry species.
The structure of F-actin was preserved prior to visualisation, with minimal loss of free myosin, by incubating cells (45 sec) with buffer containing NaCl, 137 mM; KCI, 5mM; [Na.sub.2]HP[O.sub.4], 1.1 mM; K[H.sub.2]P[O.sub.4], 0.4 mM; NaHC[O.sub.3], 4 mM; glucose, 5.5 mM; Mg[Cl.sub.2], 2 mM; EGTA, 2 mM; PIPES, 5 mM; pH 6.0-6.1 [25,26] supplemented with 0.32 M sucrose, 0.1% Triton X-100, and 1 [micro]g/mL phalloidin [27].
"Our results suggest that myosin VI may be critical in starting and maintaining the malignant properties of the majority of human prostate cancers diagnosed today," said Angelo M.
Myo3a and Myo3b double knock-out mice are profoundly deaf, demonstrating that class III myosins play redundant roles in hearing function [41].
Hammer III, "Functions of unconventional myosins," Current Opinion in Cell Biology, vol.