THE RELATION BETWEEN STRUCTURE AND FUNCTION IN HEMOGLOBINS

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Abstract
Many lines of evidence indicate that the oxygenation of hemoglobin is accompanied by changes in protein structure. Data on the oxygen equilibria of the hemoglobins from a number of animals are discussed in terms of this evidence. Evidence from studies of some hemoglobins (lamprey, frog and tadpole) indicates a major role for subunit dissociation equilibria in explaining two properties of the oxygen equilibria: heme–heme interaction and the "Bohr effect". The importance of subunit dissociation in mammalian hemoglobins is suggested by the known concentration dependence of the oxygen equilibria. Mammalian hemoglobins are composed of two types of polypeptide chains, α and β. The idea that the α and β subunits have different oxygen equilibria and are affected differently by pH is examined. It is concluded that the β-chains appear to play a major role in the mechanism of the Bohr effect not shared by the α-chains. This conclusion is supported by the structural changes in hemoglobin found to occur upon oxygenation by X-ray diffraction techniques.