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Myosin myofibrils of the highest concentrations of protein, about 60% of the total muscle protein constitute the thick filament myofibrillar adenosine triphosphate enzyme activity, a molecular weight of about 480,000. Its molecule has two oval-shaped head and a rod-shaped long tail. Entire molecular length is about 160 nm, the head of about 20 nm and a width of 9 nm.

 The tail from two heavy chains (H) of the rod-shaped part in the form of a double-stranded α-helical components; head includes four light chain (L) and the end portion of the heavy chain, the molecular weight of the heavy chain of about 20 million. Now know that a total of three kinds of light chains are called L1 (molecular weight 16,000), L2 (molecular weight of 18,000 to 20,000) and L3 (2.5 million). Chinese scientists Caotian Qin was first discovered in 1953 in the UK the light chain. Each myosin molecule contains two identical the L2 chain; For the remaining two light chains, you may have three different combinations, that. Myosin molecules can have three kinds of different composition visual impact muscle building review workout

The muscles different types molecular varying quantities of the three kinds of different composition. A structure of the light chain of the rabbit and chicken skeletal muscle has been elucidated, L1 and L3, a structure is very similar to ATP enzyme activity of the protein required. L2 in the lower animals regulatory role. If removed from higher animal skeletal muscle myosin L2, its function is unchanged.

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Thick filament myosin molecules are able to gather tail of the tail and then arranged in myofibrils parallel, the head of the molecular out of the surface of the thick filament to form links with filaments "cross-bridge". The distance between the two myosin head in the striated muscle myofibrils is 14.3 nm, while the distribution cycle of the head in the coarse wire is 42.9 nm. This is the spacing between the two head facing in the same direction of the thick filament.

Smooth muscle myosin of its size and shape and skeletal muscle myosin is very similar, but there are some differences in chemical properties. Smooth muscle myosin are only two molecular weight of each of the light chain of 20,000 and 16,000, and the ability of the anti-proteolytic enzyme hydrolysis strong. ATP enzyme activity under the same conditions, the actin protein or a divalent calcium ion activation than skeletal muscle myosin. Smooth muscle myosin itself having a calcium ion regulation actomyosin reaction function, this adjustment function in skeletal troponin completed. The experimental results proved that this adjustment function and a molecular weight of the smooth muscle myosin light chain phosphorylation of 20000 relevant.

Actin myofibrils in content (20%) after a myosin contractile proteins, the it and tropomyosin, troponin regulating proteins constitute the myofibrillar the filaments. The contraction of the muscles mainly rely mutually sliding in the thickness between the filaments and achieve.

The two forms of actin, a known globular or monomeric actin (G-actin), and another by moving the fibrous protein polymerization of monomer muscle actin (F-actin). Monomeric actin protein molecular diameter of about 5.5 nm, slightly pear-shaped, and a molecular weight of 43,000. Rabbit skeletal muscle actin is constituted by 374 amino acid residues in a peptide chain, and its primary structure has been determined. Actin having the double spiral structure, and 13 monomers form 36 nm half-pitch.