Reactivity differences between haemoglobins. Part IX. Thermodynamics of the reaction of azide ion with some animal methaemoglobins

Abstract

The free energies and enthalpies of formation of the azide complexes of pigeon, dog, and guinea pig methaemoglobins have been determined as a function of pH. A characteristic feature of these reactions is the almost exact compensation between large enthalpy and entropy changes over a wide pH range, and the bell-shaped curve describing the variation of ΔH with pH. A correlation is shown to exist between the pH of maximum ΔH and the isoelectric point of any methaemoglobin.