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Biochem/physiol Actions

Myosin interacts with actin in muscle and non-muscle cells. Myosin is one of three classes of cytoskeletal motor proteins that have been identified. The others are kinesins and dyneins. These three types of proteins are thought to be responsible for the many movements that occur in cells. Myosin has been shown to be involved in neurosensory function, vesicle trafficking, determinant partitioning, and cortical function.

Myosin interacts with actin in muscle and non-muscle cells. Myosin molecules consist of two major regions: tails (rods) and heads. They aggregate into filaments through the tail region and interact with actin and with ATP through the head region. Myosin molecules spontaneously assemble into filaments in solutions of physiologic ionic strength and pH. Thick filament consists mainly of myosin molecules. Myosin is activated by the enzyme ATPase. This activation is the immediate source of the free energy that drives muscle contraction. It binds to the polymerized form of actin, the major constituent of the thin filament. Multiple forms of myosin heavy chains exist for each muscle type-skeletal, cardiac, smooth and non-muscle isomyosin forms exist in different types of skeletal muscle, depending on the physiological function of the muscle. These are designated as type I (slow-twitch) and type II (fast-twitch). Myosin is one of three classes of cytoskeletal motor proteins that have been identified. The others are kinesins and dyneins. These three types of proteins are thought to be responsible for the many movements that occur in cells. Myosin has been shown to be involved in neurosensory function, vesicle trafficking, determinant partitioning, and cortical function.

Physical form

Solution in 50% glycerol containing 0.6 M potassium chloride and 10 mM potassium phosphate buffer, pH 6.8. Note: Solution may be hazy.

Unit Definition

One unit will liberate 1.0 µmole of inorganic phosphorus from ATP per min at pH 9.0 at 25 °C in the presence of calcium.