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(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.



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.


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



A muscle protein, comprising up to 50% of the total muscle proteins; combines with actin to form actomycin.
References in periodicals archive ?
36) To examine some properties of Chara myosin light chains, we performed immunological investigation.
Another important role of the myosin light chain is regulatory function.
Four of 5 proteins were identified as myosin light chain 1 slow-twitch isoform (MLC1sa), troponin T (TnT), triosephosphate isomerase (TPI) and DJ-1 protein.
We found the several stage-related proteins such as myosin light chain, troponin T, triosephosphate isomerase and DJ-1 protein in porcine skeletal muscle, probably providing a basis for understanding the biochemical and molecular diversities of skeletal muscle during growth stages.
KEY WORDS: Litopenaeus vannamei, White Spot Syndrome Virus, WSSV, linkage mapping, expressed sequence tags, ESTs, ShrimpMap, myosin light chain, E-F hand motif, actin, ribosomal proteins
The ten polymorphic ESTs included: a putative EF-hand calcium binding domain and the FRQl protein domain of myosin light chain (TUASPvWSu233), ribosomal proteins S10 and S5, actin, troponin I, nucleoside diphosphate kinase, arginine kinase, and 3 ESTs of unknown function (Table 2).
Influence of repertusion on serum concentrations of cytosolic creatine kinase and structural myosin light chains in acute myocardial infarction.
Circulating cardiac myosin light chains in patients with angina at rest: identification of a high risk subgroup.