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Related Experiment Videos

Coupling between phosphate release and force generation in muscle actomyosin.

Y Takagi1, H Shuman, Y E Goldman

  • 1Pennsylvania Muscle Institute, University of Pennsylvania, D700 Richards Building, 3700 Hamilton Walk, Philadelphia, PA 19104-6083, USA.

Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences
|January 14, 2005
PubMed
Summary

Phosphate release from actomyosin-adenosine diphosphate phosphate (AM.ADP.Pi) in muscle fibers is reversible and linked to force generation. New structural data support a stepwise model of muscle contraction involving myosin binding, force generation, and subsequent phosphate dissociation.

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Area of Science:

  • Muscle physiology and biophysics
  • Molecular mechanisms of muscle contraction
  • Biochemistry of force generation

Background:

  • Previous studies suggested phosphate (Pi) release from actomyosin-adenosine diphosphate Pi (AM.ADP.Pi) in muscle fibers is linked to force generation and reversible.
  • The transition to the force-generating state and Pi release were hypothesized as separate but closely linked steps.
  • Early myosin crystal structures suggested rigid coupling, but didn't explain myosin's affinity for actin and nucleotides.

Purpose of the Study:

  • To investigate the role of phosphate release in muscle force generation.
  • To reconcile structural data with kinetic experiments on actomyosin interactions.
  • To elucidate the sequence of events in the myosin motor cycle.

Main Methods:

Related Experiment Videos

  • Energetic, kinetic, and oxygen exchange experiments.
  • Isometric optical clamp measurements of single actomyosin interactions.
  • Analysis of newer myosin crystal forms and structural data.

    • Main Results:

    • Phosphate (Pi) release from AM.ADP.Pi is reversible and linked to force generation in muscle fibers.
    • Pi shortens actomyosin interactions only if they last long enough (20-40 ms) for Pi to dissociate.
    • Newer structural data suggest actin-binding cleft closure opens switch I, decreasing nucleotide affinity.

    Conclusions:

    • The findings support a stepwise model of muscle contraction: myosin.ADP.Pi binds weakly, then strongly to actin, generating force.
    • Phosphate dissociation may further increase force or sliding.
    • Structural and kinetic data are consistent with a myosin motor cycle involving sequential binding, force generation, and Pi release.