Myosin refers to a family of motor proteins (other motor proteins include dynein and kinesin). To date (Feb 2001) there are 16 known proteins in this family.

All Myosin's posess a heavy chain which binds actin (which in the form of F-actin forms filaments called microfilaments that help cells move and function). While these heavy chains are not all identical, they retain a high degree of similarity across the Myosin family.

You may realize (from the Webster 1913 definition) that Myosins are particularly concentrated in cells that are specialized for motility. The myosin found in muscle cells (which actually come in three flavors of skeletal muscle, cardiac muscle, and smooth muscle and here we are referring to skeletal, but other types are relatively analogous in nature) is for the most part Myosin II.
Myosin I and II are the most abundant myosin proteins found in humans. Unlike Myosin II, Myosin I also has an actin binding site in it's tail (as well as in its head (the heavy chain)).
Other interesting myosins are Myosin 5, which is responsible for a good deal of intracellular motility and is especially essential (and highly concentrated) in the vertebrate brain ecause of it's role in transport of vacuoles essential to synaptic communication, and Mysoin 6 and Myosin 7 which are essential to the eyes an the tiny hairs in the inner ear (mutations resulting no expression or misexpression of these proteins often leads to deaf blind syndrome).

Myosin is frequently used in experiments with actin, and can be used to determine the polarity of an actin filament. By bindind Myosin S1 to F-Actin (called "Myosin decorating" by cell biologists), and then adding more G-actin and allowing polymerization, the plus end can be discerned as the side of the "decorated" (initial bit of) actin filament with a much longer undecorated tail.

To learn more about the role and importance of Myosin in muscle, you might like to read about Myosin II.

My"o*sin (?), n. [Gr. , a muscle.] Physiol. Chem.

An albuminous body present in dead muscle, being formed in the process of coagulation which takes place in rigor mortis; the clot formed in the coagulation of muscle plasma. See Muscle plasma, under Plasma.

⇒ Myosin belongs to the group of globulins. It is insoluble in water, but soluble in dilute solution of salt, and is especially characterized by being completely precipitated by saturation of its solutions with salt.


© Webster 1913.

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