(redirected from Myosins)
Also found in: Dictionary, Thesaurus, Medical.
Related to Myosins: Myosin Heavy Chain, myosin V


(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 ?
Disrupting the function of actin, Rho, Rac, Cdc42, or myosin prevents polar body formation (Halet and Carroll, 2007; Ma et al.
Studies in budding yeast revealed that myosin and dynein are molecular motors that walk along microtubules or actin filaments and can contribute to spindle positioning directly by generating a pulling or pushing force (Huisman and Segal, 2005; Person and Bloom, 2004).
Three of these ESTs amplified in mo st of the IRMF offspring and were used for linkage analysis, the EFhand motif of myosin light chain (accession #CX535935) was placed in ShrimpMap's linkage group 7, whereas ribosomal protein S5 (accession #CX535957) and troponin I (accession #CX535976) remained unassigned.
In summary, various EST sequences representatives of calcium, glycolytic, and proteins synthesis pathways were identified, primers were designed from ESTs regions flanking single or multiple SSRs with three or more repeats, and so far, the gene encoding the EF-hand calcium-binding domain of myosin light chain has been mapped to linkage group 7.
Cellular Metabolic Process / putative or Known Genes # of Clones (a) Cytoskeleton mRNAs Actin 30 Tropomyosin (shrimp 2 allergen, involved in actin-binding and muscle contraction) Troponin C 1 Troponin I (similar to 12 Drosophila wupA, has actin-binding activity) Myosin heavy chain-fast 4 Spectrin repeats (c)--Muscle 2 specific protein 300 (actin-binding activity) Spectrin repeats, Actinin 1 alpha (flightless-A, F- actin cross-linking protein) Calcium ion balance (also cytoskeleton mRNAs) Partial homology to putative 3 orthologs of Myosin light chains (MLC1, MLC2, myosin regulatory light chain)--some include EF-hand Cat + binding motif.
Luo added that by using myosin VI or other factors, it may be possible to create a laboratory test to identify high or low levels in urine or blood samples, which might aid in the detection of prostate cancer.
Myosin VI also has been shown to be associated with ovarian cancer.
7-fold higher expression of myosin VI as compared to normal samples, and a 4.
Researchers next hunted for myosin VI in 240 prostate tissue samples, discovering overproduction early in the development of prostate cancer in such pre-tumor conditions as high-grade prostatic intraepithelial neoplasia (PIN) and proliferative inflammatory atrophy.
Cytokinetics recently initiated a Phase I human clinical trial with CK-1827452, a novel small molecule cardiac myosin activator, for the treatment of heart failure.