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Intermediate complex of ATP hydrolysis and synthesis by muscle proteins
Journal of Supramolecular Structure
|January 1, 1975
Abstract:
Myosin catalyzed exchange between 32Pi and ATP in reaction medium during its enzymatic hydrolysis of ATP only by a very small amount. Addition of actin increased to a great extent the rate of incorporation of 32Pi in the presence of Mg. Glycerinated smooth muscle fibers also exhibited the ability to exchange 32Pi and ATP upon the application of external force (repeated stretching and releasing). A schematic mechanism of the action of actin and external force on acceleration of 32Pi incorporation is proposed and the importance of the M-ADP complex for force generation is suggested.
Insights
Myosin
Area of Science:
- Biochemistry and Muscle Physiology
Background:
- Muscle contraction involves the enzymatic hydrolysis of adenosine triphosphate (ATP) by myosin.
- Understanding the kinetics of ATP hydrolysis and phosphate exchange is crucial for elucidating muscle function.
Purpose of the Study:
- To investigate the role of actin and mechanical force in modulating the exchange of inorganic phosphate (32Pi) with ATP during myosin's enzymatic activity.
- To propose a mechanism for force generation in muscle fibers.
Main Methods:
- Enzymatic assays measuring the incorporation of 32Pi into ATP catalyzed by purified myosin.
- Experiments involving the addition of actin and magnesium ions to the reaction medium.
- Mechanical stimulation (stretching and releasing) of glycerinated smooth muscle fibers to assess 32Pi and ATP exchange.
Main Results:
- Myosin alone showed minimal ATP-catalyzed 32Pi exchange.
- Actin significantly accelerated 32Pi incorporation in the presence of Mg.
- Glycerinated muscle fibers demonstrated 32Pi and ATP exchange upon application of external force.
Conclusions:
- Actin and external mechanical force enhance the rate of 32Pi incorporation, suggesting their involvement in the myosin ATPase cycle.
- A model is proposed where the myosin-ADP complex plays a key role in force generation during muscle contraction.