Functional characterization of the single hemoglobin of the migratory bird Ciconia ciconia

Hemolysate from white stork displayed a single hemoglobin component, thus resulting into two bands and two globin peaks in dissociating PAGE and reversed phase-HPLC, respectively. Stripped hemoglobin showed an oxygen affinity higher than that of human HbA, a small Bohr effect, and a cooperative oxygen binding. A small decrease of oxygen affinity, of the same extent in all the pH range examined, was observed by addition of chloride, thus indicating an unusual chloride-independent Bohr effect (ΔlogP50 / Δlog pH = - 0.24). Saturating amounts of inositol hexakisphosphate, largely decreased hemoglobin-oxygen affinity (ΔlogP50 = 1.17 at pH 7.0), and increased the extent of its Bohr effect (ΔlogP50 / ΔlogpH = - 0.45). The phosphate binding curve allowed to measure a very high overall binding constant (K = 1.18 × 105 M- 1). The effect of temperature on the oxygen affinity was measured, and the enthalpy change of oxygenation resulted almost independent on pH. Structural-functional relationships are discussed by considering some amino acid residues situated at α1/β1 and α1/β2 interfaces, such as α38 and α89 positions. The presence of only one hemoglobin component, a rare event among birds, and its functional properties have been related to the physiological oxygen requirements of this soaring migrant bird and to its technique of flight during migration