Also found in: Dictionary, Thesaurus, Medical, Acronyms, Wikipedia.
Related to myosin: Myosin light chain kinase


(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.
..... Click the link for more information.
 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.
..... Click the link for more information.
. 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
..... Click the link for more information.
. 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
..... Click the link for more information.
, 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 ?
In related work, Overturf has created real-time PCR assays for analyzing nearly two dozen other gene-derived natural compounds in trout--in addition to myosin.
Thus, myosin was purified rapidly (within 2 days) to a high level (>95% by SDS-PAGE) and in high yield (about 10mg/100g packed wet cells).
Non-radioactive reverse transcriptase/polymerase chain reaction for quantification of myosin heavy chain mRNA isoforms in various rabbit muscles.
A type VII myosin encoded by the mouse deafness gene shaker-I.
Individual ATP hydrolysis cycles for a single myosin were measured using a fluorescent ATP analog, Cy3-ATP, (21),(22) which is hydrolyzed the same way as ATP in solution.
Stable and dynamic microtubules coordinately shape the myosin activation zone during cytokinetic furrow formation.
The contractive characteristics of mammal skeletal muscles are determined by myosin heavy chain (MHC) subtypes.
Regulation of cytoskeletal mechanics and cell growth by myosin light chain phosphorylation," American Journal of Physiology--Cell Physiology, vol.
In our model, actin filaments can be manually slided over myosin filaments as is given in the sliding filament theory of muscle contraction and Z disc also move along with movement of actin filaments.
We first examined changes in the expression of the myosin heavy chain isoforms MyHC I, MyHC IIA, MyHC IIB and MyHC IIX, following 8 weeks of moderate or high intensity treadmill exercise, using SDS-PAGE.
These proteins were categorised into 7 types, namely; tropomyosin-1 alpha chain (TPM1), actin - alpha cardiac muscle 1 (ACTC), myosin light chain 3 - skeletal muscle isoform (MLC3F), myosin regulatory light chain2 - skeletal muscle isoform (MLC2F), myoglobin, troponin T - fast skeletal muscle (TnTf), and creatine kinase M chain (M-CK).
The secondary FITC-conjugated anti-mouse antibody (Sigma) at 1:100 dilution for anti a actinin, myosin heavy chain, and cardiac troponin T and FITC-conjugated donkey anti-rabbit antibody (Santa Cruz) for atrial natriuretic peptide with the same dilution were used.