Actin myosin complex

Rayment, 1., et al. Structure of the actin-myosin complex and its implications for muscle contraction. Science 261 58-65, 1996. 

Rayment, L, Holden, H.M., Whittaker, M., Yohn, C.B., Lorenz, M., Holmes, K.C., Milligan, R.A. (1993b). Structure of the actin-myosin complex and its implications for muscle contraction. Science 261, 58-65. 

In addition to its effects on enzymes and ion transport, Ca /calmodulin regulates the activity of many structural elements in cells. These include the actin-myosin complex of smooth muscle, which is under (3-adrenergic control, and various microfilament-medi-ated processes in noncontractile cells, including cell motility, cell conformation changes, mitosis, granule release, and endocytosis. 

Myosin-ATP has a low affinity for actin, and actin is thus released. This last step is a key component of relaxation and is dependent upon the binding of ATP to the actin-myosin complex. 

N ow that some of the major types of protein structures have been described it is appropriate to turn to the question of how protein structure relates to protein function. To explore this question, two protein systems, hemoglobin and the actin-myosin complex, are examined in detail. 

M. Lorenz, K. C. Holmes, and R. A. Milligan, Structure of the Actin-Myosin Complex and Its Implications for Muscle Contraction. Science 261 58-65, 1993. 

Szent-Gyorgyi discovered actin and the actin-myosin complex. 

Using the fit of myosin V into the cryoelectron microscope density as the basis of the rigor complex, by adding back the missing lever arm one can generate the model of the end-of-powerstroke actin-myosin complex shown in Fig. 5 (Holmes et al, 2004). 

In a muscle homogenate, actin-myosin was found to have formed complexes that were able to settle on the chromatographic material. Moreover, the actin-myosine complexes bound various glycolytic enzymes.20 An elution profile resulting when lactate dehydrogenase was being purified from muscle homogenate is shown in Fig. 3. 

The molecular events underlying the contraction of muscle involves release of calcium ions from the sarcoplasmatic reticulum as a result of acetylcholine release from the corresponding nerve. Binding of ATP to the myosin heads is the first step in the cycle of relative movement of actin/myosin. Following that, ATP-myosin heads bind to actin molecules, dephosphorylation (the myosin head also functions as an ATP-ase) and dissociation of the actin-myosin complex and... 

However, a nerve impulse to the muscle triggers a release of Ca2+ from the sarcoplasmic tubular system, where it is ordinarily bound, which increases the intracellular Ca2+ concentration to 10 5-10 6M. This level of Ca2+ allows the actin in the thin filament to accept the energized-ADP-myosin cross-bridge to initiate contraction. As each cross-bridge completes the swivel part of its cycle, it loses the bound ADP and immediately accepts a molecule of ATP that is always supplied to living muscle. The ATP immediately causes a dissociation of the actin-myosin complex, and the myosin catalyzes the hydrolysis of ATP to yield the myosin—ADP energized state again, ready to repeat the cycle. 

Contraction can be indicated as in Equation 11.87, where the sliding process involves dissociation of an actin-myosin complex. When relaxation occurs the sliding process is reversed and the complex is re-formed, again utilising energy from the ATP. 

The release of mechanical energy by muscle contraction is the result of a motile biosystem, of protein constitution, namely actin-myosin complex. This one is able of chemomechanical transformations that occur far from equilibrium and are enzymatically caused, external commanded by a trigger agent, Ca and transmitted to a macrofag, ATP, located in its proximity. In turn, ATP is partially... 

The ATP insufficiency or disappearance causes muscular rigidity. Whenever the level of ATP is overtaken into the muscular cell, and the concentration Ca++ intracellular, Ca, is no further control-led, a rigor state is entered whereby actin and myosin interact to form a very stiff connection. Therefore, the role of ATP in muscle contraction is that of dissociating of actin-myosin complex but not of its formation. The flux of Ca ions is of peculiar importance in the release of movement and in sarcomere it is controlled by a sequence of events. 

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