Electrostatic effects in hemoglobin: Bohr effect and ionic strength dependence of individual groups

Area of Science:

• Biochemistry
• Physical Chemistry

Background:

• Human hemoglobin exists in two quaternary states: deoxyhemoglobin and oxyhemoglobin.
• The Bohr effect describes the influence of pH on hemoglobin's oxygen affinity.
• Understanding electrostatic interactions is crucial for explaining hemoglobin's functional properties.

Purpose of the Study:

• To compute the alkaline Bohr effect of human hemoglobin at varying ionic strengths.
• To apply electrostatic treatment to explain proton binding differences between deoxyhemoglobin and oxyhemoglobin.

Main Methods:

• Utilized electrostatic treatment applied to titration behavior of individual groups.
• Calculated the alkaline Bohr effect at ionic strengths of 0.01 M and 0.10 M.
• Incorporated the effects of bound anions at higher ionic strength.

Main Results:

• Electrostatic treatment successfully accounted for enhanced proton binding in deoxyhemoglobin.
• The number of contributing groups to the Bohr effect varied with ionic strength (10 at 0.10 M, 28 at 0.01 M).
• Differences in electrostatic behavior stem from charge and solvent accessibility dissymmetries between the two hemoglobin states.

Conclusions:

• Electrostatic treatment provides a framework for understanding the Bohr effect in human hemoglobin.
• Ionic strength and bound anions significantly influence the electrostatic contributions to the Bohr effect.
• Structural dissymmetries between deoxy- and oxyhemoglobin are key to their differing electrostatic properties.