Dynamic Light Scattering Study of Muscle F-Actin in Solution
G-actin is globular in shape (Fig. 1a). Its molecular weight is about 42k daltons. G-actin polymerizes into F-actin under physiological salt concentrations (Fig. 1b). Based on observations by electron microscopy, a “pearl-and-necklace” model is proposed for the ultrastructure of F-actin. F-actin is a two-stranded helical polymer. The half pitch of the helix is 35 nm and within this length, there are 13 G-actins. The total length of F-actin varies according to polymerization conditions and, roughly speaking, is longer than 1 pm. As might be supposed from its structure, F-actin is rather stiff. Electron micrographs show the images of gradually curved F-actin. Tropomyosin is a rodlike protein (Fig. lc). When tropomyosin molecules are added to the solution of F-actin, they bind to F-actin and settle in the grooves of F-actin helix forming tropomyosin strands (Fig. ld). Myosin has two heads called subfragment-1 (S-1) and binds to F-actin in the absence of ATP. Partial digestion by some kind of proteases produces heavy meromyosin (HMM) and also S-1 (Fig. le).
KeywordsAdductor Muscle Coherence Polystyrene Autocorrelation Macromolecule
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