Abstract
Abstract As part of an ongoing survey, the early time region of hemoglobin's hydrogen exchange curve was studied to find hydrogens that respond to allosteric structure change. A difference hydrogen exchange method, previously designed for this kind of study, was used. Among the approximately 25 hydrogens per subunit studied, 7 respond to ligand binding by accelerating 14-fold in exchange rate; the remainder are ligand-indifferent. The responsive hydrogens form a first order kinetic class in both liganded and deoxyhemoglobin, and this gives further support to the breathing picture of hydrogen exchange. The increase in exchange rate observed indicates that the segment holding these hydrogens experiences a net structural free energy change worth +1.5 Cal in the allosteric transition.
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