KINETIC AND EQUILIBRIUM STUDIES OF LIGAND BINDING TO HEMOGLOBIN VARIANTS

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The aim of this project is the characterization of the functional properties of variants of human hemoglobin by examination of the equilibria and kinetics of their reactions with ligands. The purpose of this undertake is to contribute to the further development and testing of predictive stereochemical model which has been developed by this Program Project. Hemoglobin variants, as well as hemoglobins containing two different alphabeta dimers (mixed-mutant hybrid hemoglobins) and hemoglobins containing different metalloporphyrins (mixed-metal hybrids), will be prepared by Core C, using site directed mutagenesis and expression of globin chains in E. coli., followed by isolation and assembly. Equilibria of oxygen binding in solution to the mutant hemoglobins will be measured. Kinetic studies will be carried out using stopped-flow and flash photolysis techniques to examine the effects of mutations on the properties of the R and T quaternary states of the hemoglobin molecule, the relative stabilities of these states and the stability of the tetramer with respect to dissociation into alphabeta dimers. Properties of the T states of these materials will also be examined by measuring the equilibria of oxygen binding to T state crystals grown in polyethylene glycol as well as to T state molecules embedded in silica gels. Properties of the alpha and beta chains of hemoglobin variants within the T quaternary state, and the functional properties of partially liganded hemoglobin variants will be assessed by examining the equilibrium and kinetic properties of symmetric and asymmetric mixed-metal and mixed-mutant hybrid hemoglobins.