The Actomyosin ATPase: A Two-State System [and Discussion]

Studies of the interaction between actin and myosin subfragment 1 (S1) in solution have shown that the association reaction takes place in at least two steps. Initially the association is relatively weak to form a complex called the A state which can then isomerize to the R state. The rate and equil...

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Bibliographic Details
Published in:Philosophical transactions of the Royal Society of London. Series B. Biological sciences 1992-04, Vol.336 (1276), p.63-71
Main Authors: Geeves, M. A., Elliott, G. F., Sleep, J. A., Goody, R., Dutton, P. L.
Format: Article
Language:English
Subjects:
Actins
Adenosine triphosphatases
Animals
Binding Sites
Biochemistry
Calcium
Fluorescence
In Vitro Techniques
Isomerization
Kinetics
Models, Biological
Muscle contraction
Muscle Contraction - physiology
Muscle fibers
Myosins - chemistry
Myosins - metabolism
Nucleotides
Tropomyosin - metabolism
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Summary:Studies of the interaction between actin and myosin subfragment 1 (S1) in solution have shown that the association reaction takes place in at least two steps. Initially the association is relatively weak to form a complex called the A state which can then isomerize to the R state. The rate and equilibrium constants for the isomerization have been measured and are shown to depend upon the nucleotide bound to the S1 ATPase site; with ATP bound the A state is preferred but as ATP is hydrolysed and the products are sequentially released then the complex gradually shifts to the A state. An extensive series of experiments have characterized the A-to-R isomerization both in solution and in contracting muscle fibres and have shown it to be closely associated with the key events in the ATP-driven contraction cycle: the conformational change from the A to the R state can be monitored by fluorescent probes on either actin or the nucleotide; the isomerization can be perturbed by increases in hydrostatic pressure; the actin-induced acceleration of the rate of product release from myosin is coupled to the A-to-R isomerization; tropomyosin may control actin and myosin interaction by controlling the ismoerization step and finally pressure perturbations of contracting muscle fibres shows there to be a close coupling between the isomerization of acto.S1 and the force generating event of muscle contraction.
ISSN:0962-8436
1471-2970
DOI:10.1098/rstb.1992.0045