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Related Experiment Videos

A tertiary two-state allosteric model for hemoglobin.

Eric R Henry1, Stefano Bettati, James Hofrichter

  • 1Laboratory of Chemical Physics, Building 5, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0520, USA.

Biophysical Chemistry
|July 20, 2002
PubMed
Summary
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The tertiary two-state (TTS) model explains hemoglobin

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Biophysics

Background:

  • The Monod, Wyman, and Changeux (MWC) model accurately describes hemoglobin's homotropic effects.
  • However, the MWC model fails to explain heterotropic effects observed experimentally.
  • Existing explanations attribute this to tertiary conformational changes without quaternary shifts.

Purpose of the Study:

  • To propose and validate a new allosteric model for hemoglobin function.
  • To explain heterotropic effects by focusing on tertiary subunit conformations.
  • To reconcile kinetic and equilibrium binding data with allosteric regulation.

Main Methods:

  • Development of the 'tertiary two-state (TTS)' model.
  • Quantitative analysis of kinetic data from carbon monoxide photodissociation experiments.

Related Experiment Videos

  • Comparison of model predictions with experimental data from oxygen binding studies.

    • Main Results:

    • The TTS model successfully explains kinetic data from ~1 microsecond photodissociation experiments.
    • The model aligns with solution, gel, and single crystal oxygen binding studies.
    • The TTS model underestimates doubly-liganded molecule populations in low-temperature electrophoresis.

    Conclusions:

    • The TTS model offers a viable alternative to the MWC model for explaining hemoglobin allostery.
    • Tertiary subunit conformations, rather than quaternary structures, are key to heterotropic effects.
    • Further refinement considering conformational substates may improve sub-microsecond kinetic data agreement.