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<p>In this study, the thermodynamics of the one-electron (Fe<sup>2+</sup>/Fe<sup>3+</sup>) oxidation-reduction of the heme-bound fluoride complexes of adult hemoglobin (Hb-F) and horse heart myoglobin (Mb-F) were addressed to interpret the molecular changes these proteins undergo during the redox reactions. We measured the enthalpy (Δ<i>H</i><sup>o’</sup>) and entropy (Δ<i>S</i><sup>o’</sup>) of these reactions at pH 5 and pH 7, and also for the oxidation-reduction reactions of the metaquo complexes and for fluoride binding. The temperature dependence of the reduction potentials (<i>E</i><sub>m</sub>) of Hb-F and Mb-F showed two redox pathways with distinct thermodynamic properties in the 5 to 45&#xa0;°C temperature range, but only at pH 5. The <i>E</i><sub>m</sub>-<i>T</i> plots of Hb-F and Mb-F were complementary to each other, with opposing signs in their Δ<i>H</i><sup>o’</sup> and Δ<i>S</i><sup>o’</sup>. The redox reactions of the metaquo heme complexes and the heme-bound fluoride complexes (at pH 7) show no evidence of a bifurcated redox pathway. Given the similarities of the heme-ligand structures of oxy- and fluoride-bound complexes and comparable thermodynamics between oxidation and oxygen binding equilibrium, we theorize that one of the thermodynamic pathways is for stabilization of the heme-bound fluoride complex upon the redox change and the other is associated to a redox pathway that stabilizes the heme ferrous state, a route presumably associated to the unligated heme ferric-to-ferrous equilibrium. The serendipitous mixing of these redox pathways in the heme-bound fluoride complexes highlights the specificity of the heme proteins for oxygen binding and the possible use of these pathways for their respective physiological roles of storage and transport. The thermodynamics of the redox reactions of the heme-bound fluoride complexes of hemoglobin and myoglobin exhibit properties similar to those of their oxygen binding equilibria, which govern transport and oxygen storage.</p> Graphical Abstract <p>The thermodynamics of the redox reactions of the heme-bound fluoride complexes of hemoglobin and myoglobin exhibit properties similar to those of their oxygen binding equilibria, which govern transport and oxygen storage.</p> <p></p>

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Redox implications of oxygen binding in hemoglobin and myoglobin: Thermodynamics of the (Fe3+/Fe2+) oxidation-reduction of heme-bound fluoride complexes versus fluoride binding

  • 期刊论文

  • 发表日期：

    2026年7月17日

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  • Kayla Flanders,
  • Annie Mathew,
  • Mary Lockwood,
  • Ashley Frankenfield,
  • David Deysher,
  • Kimberly Wodzanowski,
  • Tanaka Mada,
  • Thomas Nagle,
  • Jose Cerda

摘要

In this study, the thermodynamics of the one-electron (Fe2+/Fe3+) oxidation-reduction of the heme-bound fluoride complexes of adult hemoglobin (Hb-F) and horse heart myoglobin (Mb-F) were addressed to interpret the molecular changes these proteins undergo during the redox reactions. We measured the enthalpy (ΔHo’) and entropy (ΔSo’) of these reactions at pH 5 and pH 7, and also for the oxidation-reduction reactions of the metaquo complexes and for fluoride binding. The temperature dependence of the reduction potentials (Em) of Hb-F and Mb-F showed two redox pathways with distinct thermodynamic properties in the 5 to 45 °C temperature range, but only at pH 5. The Em-T plots of Hb-F and Mb-F were complementary to each other, with opposing signs in their ΔHo’ and ΔSo’. The redox reactions of the metaquo heme complexes and the heme-bound fluoride complexes (at pH 7) show no evidence of a bifurcated redox pathway. Given the similarities of the heme-ligand structures of oxy- and fluoride-bound complexes and comparable thermodynamics between oxidation and oxygen binding equilibrium, we theorize that one of the thermodynamic pathways is for stabilization of the heme-bound fluoride complex upon the redox change and the other is associated to a redox pathway that stabilizes the heme ferrous state, a route presumably associated to the unligated heme ferric-to-ferrous equilibrium. The serendipitous mixing of these redox pathways in the heme-bound fluoride complexes highlights the specificity of the heme proteins for oxygen binding and the possible use of these pathways for their respective physiological roles of storage and transport. The thermodynamics of the redox reactions of the heme-bound fluoride complexes of hemoglobin and myoglobin exhibit properties similar to those of their oxygen binding equilibria, which govern transport and oxygen storage.

Graphical Abstract

The thermodynamics of the redox reactions of the heme-bound fluoride complexes of hemoglobin and myoglobin exhibit properties similar to those of their oxygen binding equilibria, which govern transport and oxygen storage.