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Is the chemomechanical energy transformation reversible?
Pflugers Archiv : European Journal of Physiology
|June 22, 1976
Summary
Muscle contraction involves an energy-rich intermediate. Stretching insect muscle fibers with ATP showed increased phosphate incorporation into ATP during work, suggesting a transient actomyosin-ADP intermediate formation.
Area of Science:
- Muscle physiology
- Biochemistry
- Biophysics
Background:
- Muscle contraction relies on ATP hydrolysis.
- The mechanical work performed by muscles is linked to ATP turnover.
- Understanding the biochemical steps during muscle work is crucial.
Purpose of the Study:
- To investigate the incorporation of inorganic phosphate (32Pi) into ATP.
- To correlate this incorporation with mechanical work and ionic conditions in insect muscle.
- To identify potential energy-rich intermediates during muscle contraction.
Main Methods:
- Glycerol-extracted insect fibrillar muscle preparation.
- Measurement of 32Pi incorporation into ATP under varying mechanical loads (oscillatory work) and ionic conditions (calcium concentration).
- Analysis of ATPase activity, tension, stiffness, and frequency dependence of muscle fiber stretches.
Main Results:
- Increased calcium ion concentration enhanced 32Pi incorporation, ATPase activity, tension, and stiffness.
- Optimal oscillatory work at 5 Hz sinusoidal stretch doubled the 32Pi incorporation rate.
- Phosphate incorporation occurred even when work was done on the muscle and showed frequency dependence, peaking shortly after stretching.
Conclusions:
- Muscle stretching induces the formation of a transient, energy-rich intermediate, likely actomyosin-ADP.
- This intermediate accumulates briefly after stretching during the contraction cycle.
- The rate of ATP synthesis is coupled to the mechanical state and work performed by the muscle.