Myosin fibers

Actin and myosin fibers or filaments make possible the contraction of muscles. Actin and myosin fibers in muscle lie side by side and react chemically, sliding together and apart to shorten and lengthen in response to energy from adenosine triphosphate. 

Ca (and pathological Ba) action on tertiary structure of actin and myosin fibers in muscles, to be relieved by Mg + as a better complex center) or their contributions to supporting structures such as algal skeletons (SrSO in some dinoflagellates). Here, catalytic flexibility is low or non-existent, testified by extreme values of both X andc. 

MFBs synthesize far more actin fibers than standard fibroblasts, and also have myosin fibers that, when interacting with actin, constitute the contractile motor activity of MFBs. MFBs are found in healing tissue, of which they form 40% of the total number of fibroblasts present. A large number of MFBs are also foimd in the periprosthetic capsule of encapsulated breast implants, while there is no evidence of MFBs if no capsule has formed around the prosthesis. In pathology, abnormal quantities of MFBs are found in diseases such as pulmonary fibrosis and Crohn s disease. Many SMCs respond to a kind of paracrine stimulation, where the mediator is released into the environment of the target cells and diffuses towards the cell, where it interacts with a membrane receptor. 

Diffusion within cells is even more complex than within simple gels first the cytoplasm is a molecularly crowded zone, a complex gel with structural obstacles such as actin and myosin fibers and strands. There is the additional tortuosity that occurs in gels as the moving particle avoids the regions of the macromolecular chains and the obstruction effects from the impenetrable regions of the cytoplasm. If we designate as the effective... 

F. 1 Huxley s model for how a eyelie binding of myosin to actin (with rale/ (jc)) and release of actin (with rate g(x)) can cause net translatirai of the actin, and ultimately leads to contractirai of the actin-myosin fiber bundle... 

The distribution of the energy demand within the LV wall is calculated by utilizing the mechanical parameters given by the mechanical model and the theory of cross-bridges kinetics across the actin and myosin fibers of the sar-... 

Human muscles are composed of actin/myosin fibers, thereby realizing a precise motion by the sliding action of the fibers. Real applications of photomechanical systems should be possible if the material would be in a fibrous state, and thus the optical response of crosslinked photochromic liquid ciystalline polymer fibers has... 

In three-dimensional embedding space, it is f = Iclk T, where is the Boltzmaim constant and T is the temperature. Thus, since ic is a material parameter and if Tis fixed (e.g., room temperature), this result implies that f = const, independent of 1. Therefore, free DNA, RNA chains, and also some protein complexes such as myosin fibers and actin filaments, contained in the cytoskeleton of cells, can typically be well characterized and identified by their persistence length. 

Microfilaments and Microtubules. There are two important classes of fibers found in the cytoplasm of many plant and animal ceUs that are characterized by nematic-like organization. These are the microfilaments and microtubules which play a central role in the determination of ceU shape, either as the dynamic element in the contractile mechanism or as the basic cytoskeleton. Microfilaments are proteinaceous bundles having diameters of 6—10 nm that are chemically similar to actin and myosin muscle ceUs. Microtubules also are formed from globular elements, but consist of hoUow tubes that are about 30 nm in diameter, uniform, and highly rigid. Both of these assemblages are found beneath the ceU membrane in a linear organization that is similar to the nematic Hquid crystal stmcture. 

Proteins can be broadly classified into fibrous and globular. Many fibrous proteins serve a stmctural role (11). CC-Keratin has been described. Fibroin, the primary protein in silk, has -sheets packed one on top of another. CoUagen, found in connective tissue, has a triple-hehcal stmcture. Other fibrous proteins have a motile function. Skeletal muscle fibers are made up of thick filaments consisting of the protein myosin, and thin filaments consisting of actin, troponin, and tropomyosin. Muscle contraction is achieved when these filaments sHde past each other. Microtubules and flagellin are proteins responsible for the motion of ciUa and bacterial dageUa. 

Fibrous proteins can serve as structural materials for the same reason that other polymers do they are long-chain molecules. By cross-linking, interleaving and intertwining the proper combination of individual long-chain molecules, bulk properties are obtained that can serve many different functions. Fibrous proteins are usually divided in three different groups dependent on the secondary structure of the individual molecules coiled-coil a helices present in keratin and myosin, the triple helix in collagen, and P sheets in amyloid fibers and silks. 

Muscle fibers contain myosin and actin which slide against each other during muscle contraction... 

Szent-Gyorgyi further showed that the viscosity of an actomyosin solution was lowered by the addition of ATP, indicating that ATP decreases myosin s affinity for actin. Kinetic studies demonstrated that myosin ATPase activity was increased substantially by actin. (For this reason, Szent-Gyorgyi gave the name actin to the thin filament protein.) The ATPase turnover number of pure myosin is 0.05/sec. In the presence of actin, however, the turnover number increases to about 10/sec, a number more like that of intact muscle fibers. 

Muskel-. muscular, myo-, -eiweiss, n, myosin, -empfindung, /, muscular sensation, -farb-stoff, m. muscle pigment, -faser,/, muscular fiber, -fleisch, n, muscular substance, -ge-webe, n. muscular tissue, -gift, n, muscle poison, -lehre, /, myology, -masse, /. muscular substance, -saft, m. muscle juice,. -stoff, m. sarcosine. -zucker, m. inositol. Muskowit, Muskovit, m. (Min.) muscovite, muss, pr. 1 tS 3 sing, (of miissen) must. 

Fibronectin receptor is a two-chain glycoprotein of the integrin family that serves as a transmembrane linker by binding to talin on the cytoplasmic side and to fibronectin on the external side of the membrane. The pull exerted by stress fibers on attached structures may be produced by bipolar assemblies of nonmuscle myosin molecules producing a sliding of actin filaments of opposite polarity. 

It is most unlikely that the sole functions of mysoin-Il in nonmuscle cells are to provide the contractile force to bisect cells during cytokinesis and for the contractility of stress fibers. Myosin-II is present in a variety of cell types at moderate concentrations in tissues such as brain, which are almost totally non-mitotic and do... 

Kolega, J., Taylor, D.L. (1993). Gradients in the concentration and assembly of myosin II in living fibroblasts during locomotion and fiber transport. Mol. Biol. Cell 4, 819-836. 

Skeletal muscle contains three types of fiber fast-twitch oxidative glycolytic (type 2A), fast-twitch glycolytic (type 2B), and slow-rwitch oxidative fibers (type 1). The proportion of each fiber type varies in different muscles. Different fiber types contain different isoforms of myosin, although there is no evidence that their mitochondria differ qualitatively. It has been reported that there are differences between subsarcolemmal mitochondria and those deeper in the same fiber but this has been questioned (see Sherratt et al., 1988 for references). 

All these experiments were carried out with actin and myosin in solution, either using moderate ionic strength and low actin concentrations (Lymn and Taylor, 1971) or using low ionic strength and high actin concentrations (Stem et al., 1979). However, in muscle both the actin concentration and the ionic strength are high. To confirm these models, these same experiments need to be carried out in muscle fibers. 

In summary, therefore, solution and fiber biochemistry have provided some idea about how ATP is used by actomyosin to generate force. Currently, it seems most likely that phosphate release, and also an isomerization between two AM.ADP.Pj states, are closely linked to force generation in muscle. ATP binds rapidly to actomyosin (A.M.) and is subsequently rapidly hydrolyzed by myosin/actomyosin. There is also a rapid equilibrium between M. ADP.Pj and A.M.ADP.Pj (this can also be seen in fibers from mechanical measurements at low ionic strength). The rate limiting step in the ATPase cycle is therefore likely to be release of Pj from A.M.ADP.Pj, in fibers as well as in solution, and this supports the idea that phosphate release is associated with force generation in muscle. 

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