title: Heme reactivity of hemoglobins. Azide and fluoride binding equilibria of free and mercuriated ferri-gamma chains.
abstract: The free gamma chains, isolated from human foetal hemoglobin, are stable when oxidized and thus suitable for ligand binding and subunit equilibrium studies. The metaquo-ferri chains, with cysteine-F9 in the free state II ag gamma SH) possess several properties which are different from those of their p-mercuribenzoate derivative (III aq gammaSHgR); these are: stronger binding of a high-field ligand (N3- minus), altered spin equilibrium and an altered subunit equilibrium. A quantitative assessment of the free energy changes associated with all individual steps involved in changing the metaquo chains to their azide derivatives has been made. The results show that the higher apparent reactivity of III ag gammaSH (compared to IIIaq gammaSHgR) for the azide ion is not solely due to compensatory effects arising from differences of subunit dissociation or of spin equilibrium: other process(es) occurring in the ligand binding site have to be considered.
mesh_terms: D001386:Azides / Q000097:blood*; D001665:Binding Sites; D002151:Calorimetry; D003545:Cysteine / Q000032:analysis; D004578:Electron Spin Resonance Spectroscopy; D005260:Female; D005290:Ferric Compounds / Q000032:analysis; D005319:Fetal Hemoglobin; D005459:Fluorides / Q000097:blood*; D006418:Heme; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008024:Ligands; D046911:Macromolecular Substances; D008626:Mercuribenzoates; D008628:Mercury / Q000097:blood*; D010084:Oxidation-Reduction; D011247:Pregnancy; D011485:Protein Binding; D011487:Protein Conformation; D013696:Temperature; D013816:Thermodynamics
chemical_list: D001386:Azides; D005290:Ferric Compounds; D008024:Ligands; D046911:Macromolecular Substances; D008626:Mercuribenzoates; D006418:Heme; D005319:Fetal Hemoglobin; D008628:Mercury; D003545:Cysteine; D005459:Fluorides