Tropomyosin molecular weight

Both the thick and thin filaments contain other proteins. For example, the thick filament contains titin (molecular weight about 3,000,000) and the thin filament contains nebulin (although not in cardiac muscle), and the regulatory proteins troponin (molecular weight about 33,000) and tropomyosin (molecular weight about 70,000). Nebulin and titin are thought to be ruler proteins, that is, they determine the overall length of the thin and the thick filament, respectively. The... 

The thin filament consists of a double tranded helix of actin molecules. The filament appears to be relatively thin, as determined by electron microscopy, accounting for the name. Troponin is part of the thin filament. It consists of a polymer of actin subunits. Each subunit has a molecular weight of 42,000. Troponin occurs as a compiex with tropomyosin, another protein of the thin filament. There is one molecule of troponin for every seven actin moiecuies in the thin fiiament- The thick filament is composed of a network of myosin molecules. Myosin has a molecular weight of 460,000 It consists of two Identical polypeptide chains. Myosin is long rather than globular or spherical. Each myosin heavy chain is associated with two myosin light chains. 

Another very long protein (nebulin) is associated with the thin filaments. Nebulin has a molecular weight of about 700,000. An abundant protein in skeletal muscle, nebulin extends from either side of the Z-disks along the entire length of the thin filaments. It may serve as a template for thin-filament assembly, and may interact with tropomyosin, and also may have a regulatory role. 

Caldesmon is a cytoplasmic protein with two isoform classes, one of which is found predominantly in smooth muscle cells and other cell types with partial myogenic differentiation. High-molecular-weight isoforms with molecular weights between 89 and 93 kD are capable of binding to actin, tropomyosin, calmodulin, myosin, and phospholipids, and they function to counteract actin-tropomyosin-activated myosin adenosine triphosphatase (ATPase). As such, they are mediators for the inhibition of calcium-dependent smooth muscle contraction." ... 

Paramyosin has, at most, 2 to 3 prolines per 220,000 molecular weight (32, 47), a weight % similar to that found for LMM Fr. I. and lower than that for tropomyosin (58). 

Rod-shaped molecules have larger frictional coefficients than do spherical molecules. Because of this, the rod-shaped tropomyosin has a smaller (slower) sedimentation coefficient than does the spherical hemoglobin, even though it has a higher molecular weight. 

Tropomyosin (ca. 5% of the contractile proteins) is a highly elongated molecule (2 x 45 nm) with a molecular weight of about 68,000, and is assumed to be a double-stranded a-helix. Although each chain contains the same number of amino acids, their sequences differ in 39 positions. Tropomyosin contains no di-sulfide bridges and... 

Actin is a one-chain globular protein with a relative molecular weight of 43.5 kDa (G-actin, where G stands for globular). This monomeric form polymerises to yield a fibrous form of actin (F-actin, where stands F for fibrous). The units of G-actin are organised into a heKx composed of two monomers. This polymer binds to the protein tropomyosin (relative molecular weight 70 kDa), which has a similar structure to the fibrillar part of myosin (two unequal polypeptide chains, essentially curled into an a-hehx). The actin is further connected to the regulatory troponins proteins (troponin complexes C, I and T) with relative molecular weights of 18,24 and 37 kDa, respectively. 

Tropomyosin forms very viscous solutions of polymeric particles. The protein can be obtained crystalline and has a molecular weight of 50,000 to 150,000 (depending on the animal species). The molecule is very asymmetric. It is a component of the myofibrils, particularly of smooth musculature. 

---