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Allosteric kinetics and equilibria differ for carbon monoxide and oxygen binding to hemoglobin
N Q Zhang1, F A Ferrone, A J Martino
1Department of Physics and Atmospheric Science, Drexel University, Philadelphia, Pennsylvania 19104.
Biophysical Journal
|August 1, 1990
Summary
This study measured the allosteric transition rates of oxyhemoglobin A, revealing distinct behaviors compared to carboxyhemoglobin. Oxygen-bound hemoglobin shows temperature-independent transitions, unlike CO-bound hemoglobin.
Area of Science:
- Biophysics
- Biochemistry
- Molecular Biology
Background:
- Hemoglobin's quaternary structure transitions between R (relaxed) and T (tense) states.
- Understanding these allosteric transitions is crucial for hemoglobin function.
- Ligand binding significantly influences hemoglobin's allosteric behavior.
Purpose of the Study:
- To measure the forward and reverse rates of the allosteric transition for oxyhemoglobin A.
- To compare the allosteric behavior of oxyhemoglobin with carboxyhemoglobin.
- To investigate the temperature dependence of these transitions.
Main Methods:
- Modulated excitation method was employed to measure transition rates.
- Experiments were conducted in pH 7 phosphate buffer.
- Data quality was superior to previous experiments using CO as a ligand.
Main Results:
- Oxyhemoglobin's allosteric transitions were essentially temperature independent.
- Carboxyhemoglobin transitions showed temperature dependence with specific activation energies.
- The T structure is favored more strongly in triligated oxyhemoglobin than carboxyhemoglobin.
Conclusions:
- Ligand-dependent differences in allosteric behavior are observed between oxyhemoglobin and carboxyhemoglobin.
- The findings are compatible with stereochemical studies.
- Discrepancies exist between experimental data and current allosteric models regarding T species populations.