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Three-state combinatorial switching in hemoglobin tetramers: comparison between functional energetics and molecular
F R Smith1, D Gingrich, B M Hoffman
1Department of Biology, Johns Hopkins University, Baltimore, MD 21218.
Summary
Hemoglobin
Area of Science:
- Biochemistry
- Molecular Biology
- Structural Biology
Background:
- Previous studies on cyanomethemoglobin revealed three distinct free energies of cooperative interaction among tetrameric species.
- The distribution of these free energies contradicts a simple two-state molecular switching mechanism.
Purpose of the Study:
- To investigate if the observed three-state cooperative switching in hemoglobin is a fundamental property.
- To explore the role of heme iron versus manganese substitution in cooperative interactions.
Main Methods:
- Studied two chemical systems mimicking intermediate oxygenation states.
- Replaced heme iron with manganese in specific hemoglobin subunits.
Main Results:
- The manganese-substituted systems exhibited the same distribution of cooperative free energies as cyanomethemoglobin.
- This indicates the three-state combinatorial switching is not unique to specific reactions or iron substitution.
Conclusions:
- The three-state combinatorial nature of cooperative switching is a fundamental property of hemoglobin.
- Findings align with crystallographic data on partially ligated hemoglobins.