Inhibition of Motility by Inactivated Myosin Heads
Muscle contraction and many other forms of cell motility, such as cell locomotion, cytoplasmic streaming, and cytokinesis, are believed to involve myosin dependent force generation. (For reviews, see Korn, 1978; Weeds, 1982). Our understanding of myosin structure and function has come largely from studies of movement of myosin relative to actin in muscle cells. The currently accepted model suggests that a myosin molecule moves on actin as it undergoes a conformational change of the head region while bound to actin (Huxley, 1969; Adelstein and Eisenberg, 1980). Myosin filaments translocate along actin filaments through a series of individual myosin movements (steps) along the actin filament. After each step, the heads release from the actin so that other mysoin heads can move the myosin filament forward. In most cells, it is currently impossible to quantify myosin movement on actin, and there has been no assay for myosin-based motility in vitro. Recently, however, an in vitro assay was developed (Sheetz ancl Spudich, 1983a,b) for measuring the movement of nonmuscle as well as muscle myosins on actin. With this assay, it is now possible to correlate myosin motility in vitro with muscle contraction and myosin ATPase activity. In the past year, the in vitro assay has been useful in defining a number of important aspects of myosin motility.
KeywordsActin Filament mYosin Head Cytoplasmic Streaming Myosin Filament Bead Surface
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