Muscle contraction energy transduction

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. 

Eisenberg, E. Hill, T.L. (1985). Muscle contraction and free energy transduction in biological systems. Science 227,999-1006. 

Chemo-mechanical transduction technically defines the use of chemical energy of ATP to produce motion, as in muscle contraction. The fundamental statement of the hydrophobic consilient mechanism regarding chemo-mechanical transduction is that the most charged, polar states disrupt hydrophobic asso-... 

Let us now consider in more detail the definitions of free energy related to enzyme reactions. Under steady state conditions, functioning enzyme complexes undergo cyclic transitions between a number of different states. These states can differ in the composition of a complex (enzyme molecule with ligands, substrates, products, low-molecular aflfectors, etc.), as well as in the conformations of an enzyme molecule. The complex s transitions are coupled with the chemical transformations of substrate molecules, the processes of association-dissociation of substrates and products, active transport of various substances, muscle contraction, etc. Most of these processes are of course associated with the energy transduction from one form to another. 

The swimming of bacteria, the flowing motion of the ameba, the rapid contraction of voluntary muscles, and the slower movements of organelles and cytoplasm within cells all depend upon transduction of chemical energy into mechanical work. 

This chapter describes the transduction of chemical energy into mechanical en-ergy—for example, the use of ATP hydrolysis to drive the contraction of muscles or to move cells, or the exploitation of transmembrane proton-motive force to rotate bacterial flagella. The authors describe how nanometer motions of proteins can be converted into the coordinated movements of cellular organelles, bacteria, and even animals themselves. 

In the most recent work, Dawson et al (1978) have extended their muscle NMR studies to investigate the biochemical factors affecting muscular fatigue. The substances most directly involved in the transduction of chemical free energy into mechanical work in contracting muscle are ATP, ADP, Pi, H, and Mg all of these substances actually take part in the actomyosin-ATPase reactions which produce contraction. PCr is also involved in normal contractions of vertebrate muscles because the ATP that is hydrolyzed is rapidly rephosphorylated at the expense of PCr by the enzyme creatine phosphotransferase. Since P NMR can monitor all of these substances simultaneously, either directly or indirectly, it becomes possible to relate changes in them to concurrent changes in the mechanical performance of muscles. 

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