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Haldane Effect

  • The Haldane Effect describes the phenomenon by which binding of oxygen to hemoglobin promotes the release of carbon dioxide. In many ways, the Haldane Effect is the mirror image of the Bohr Effect, making clear that oxygen and carbon dioxide compete for hemoglobin occupancy. This competition is a helpful biochemical feature which facilitates exchange of carbon dioxide for oxygen in the pulmonary and peripheral circulations.
  • The Haldane Effect is likely the result of two effects of oxygen binding on hemoglobin. First, binding of oxygen to hemoglobin appears to directly reduce the affinity of the protein for carbon dioxide in the form of carbaminohemoglobin. Consequently, binding of oxygen to hemoglobin displaces hemoglobin-bound carbon dioxide, facilitating elimination of carbon dioxide in the lungs.
  • Secondly, binding of oxygen renders hemoglobin a more acidic molecule thus resulting in the release of free hydrogen ions (H+). The higher concentration of free hydrogen ions following oxygen binding pushes the reversible equilibrium between bicarbonate and carbon dioxide in the direction of carbon dioxide. Consequently, binding of oxygen to hemoglobin facilitates conversion of bicarbonate to carbon dioxide in the pulmonary circulation and in turn enhances carbon dioxide elimination.