Chemomechanical transduction

Dynein, kinesin, and myosin are motor proteins with ATPase activity that convert the chemical bond energy released by ATP hydrolysis into mechanical work. Each motor molecule reacts cyclically with a polymerized cytoskeletal filament in this chemomechanical transduction process. The motor protein first binds to the filament and then undergoes a conformational change that produces an increment of movement, known as the power stroke. The motor protein then releases its hold on the filament before reattaching at a new site to begin another cycle. Events in the mechanical cycle are believed to depend on intermediate steps in the ATPase cycle. Cytoplasmic dynein and kinesin walk (albeit in opposite... 

The contractile apparatus may be thought of as the sum of those intracellular components which constitute the machinery of chemomechanical transduction. It is the set of proteins which convert the chemical energy of the terminal phosphate ester bond of ATP into mechanical work. The structure of the contractile apparatus is determined by the connections between the various protein molecules via specific binding sites or, in a minority of cases, via labile covalent linkages. The kinetics of the contractile machinery are determined by the regulation of changes in these connections. 

Although the fundamental chemomechanical transduction processes seem to be the same in all types of vertebrate muscle, contraction in smooth muscle is characterized by much greater involvement of enzymatically catalyzed control reactions. In smooth muscle the control reactions themselves involve the use of phosphorylation-dephosphorylation cycles. Moreover, they are futile in the sense they cause the expenditure of bond energy without a tangible work resultant, i.e., compounds synthesized or external work done. 

For the purpose of discussion, crossbridge regulation can be split into three overlapping sets of reactions (a) the Ca-calmodulin cascade (MLCK activation), (b) the phosphorylation-dephosphorylation cycle (the Four State Model), and (c) actin-myosin cycle (chemomechanical transduction). 

The mechanical behavior of the contractile apparatus of smooth muscle is also very similar to that of striated muscle. So that to the extent that the force-velocity curves reflect the interaction of mechanical force and the rate of enzymatic catalysis, the steps of the chemomechanical transduction cycles in the two muscles are apparently modulated in similar ways. Also relationships between the active isometric force and muscle length are very similar (except as noted above for shorter lengths). 

Controlled transformation of the chemical energy of nucleoside triphosphates into mechanical energy is called chemomechanical transduction. In addition to the actin filaments and microtubules, the motor proteins myosin and dynein or kinesin are needed for chemomechanical transduction. Several other proteins are associated with these, including regulatory proteins that control contractile activity and enzymes involved in maintaining the supply of high-energy phosphate. 

Relative Chemomechanical Transductional Efficiencies of the Electrostatic Charge-Charge Repulsion and Consilient Mechanisms by Experimental Determination of Ap, An, and fAL... 

As shown in the inset of Figure 5.34, the Hill coefficient for PMA is 0.5, whereas that of Model Protein v is 2.7. Thus, without consideration of differences in An, the relative efficiency would be 0.5/8.0 = 0.06 or one-sixteenth as efficient as the model protein. After the statement of efficiency for chemomechanical transduction immediately below, the relative efficiency of the two mechanisms will be given using Model Protein iv as the representative of the consilient mechanism. The ratio of Hill coefficients for the latter model protein is 0.5/2.7 or differing only by a factor of 5 rather than 16. The experimentally determined relative efficiency is still very large. 

Simple Comparisons of the Chemomechanical Transductional Efficiencies, Tj = fAl/ApxAn, of the Charge-Charge Repulsion and the Apolar-Polar Repulsion, AGap, Mechanisms... 

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