Oxygen-linked binding sites for inorganic anions to hemoglobin

A hemoglobin hybrid (alpha 2c beta 2 Prov) in which the alpha chains have NH2-terminal residues that have been blocked specifically by carbamylation and beta chains that have been derived from hemoglobin Providence I (beta 82 Lys leads to Asn) was prepared. This derivative shows a small but significant dependence of its oxygen equilibrium curve on the concentration of chloride, phosphate, or nitrate. These data were compared with oxygen-linked anion binding to hemoglobins A and Providence, and to the carbamylated hybrid, alpha 2c beta 2, by fitting equations to the data with the use of MULTIFIT II, a nonlinear curve-fitting program. Dependence of the anion dissociation constants from deoxygenated (KD) and fully oxygenated (Ko) hemoglobins upon the mathematical model is described. The data provide further support that Val-1 (alpha) and Lys-82 (beta) of hemoglobin are major, oxygen-linked binding sites for small inorganic anions and suggested that a third oxygen-linked site may also be present.