A comparison of the functional properties of two lepore hemoglobins with those of hemoglobin A1

Abstract

Abstract Lepore hemoglobins result from crossovers between normal beta and delta chain genes. Structural investigation of two newly discovered examples of Lepore hemoglobins revealed one of them to be structurally identical to hemoglobin Lepore Hollandia α 2 A δ 22 -x- β 50 , a rarely occurring Lepore variant, while the second had the structure of hemoglobin Lepore Boston α 2 A δ 87 -x- β 116 . Studies of the equilibrium and kinetic properties of the liganding reactions of these two Lepore hemoglobins, which differ only in three amino acid residues, and comparison of these with the known properties of hemoglobin A 1 ( α 2 β 2 ) and hemoglobin A 2 ( α 2 δ 2 ) have been carried out. A high value of n , the Hill coefficient, indicating normal heme-heme interaction, was observed in each hemoglobin along with a normal Bohr effect. However, a slight but definite increase in oxygen affinity was observed for each Lepore hemoglobin. Furthermore, kinetic studies indicated a slight but consistently increased rate of ligand combination and a somewhat decreased rate of oxygen dissociation for hemoglobins Lepore Hollandia and Lepore Boston at pH 7 and 20 °C. Apparently, the higher oxygen affinity of these Lepore hemoglobins over those of the normal hemoglobins A 1 and A 2 reflects changes of sequence that are common to both types of hemoglobin Lepore.