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 (Delta logP(50)/Delta log pH=-0.24). Saturating amounts of inositol hexakisphosphate, largely decreased hemoglobin-oxygen affinity (Delta logP(50)= 1.17 at pH 7.0), and increased the extent of its Bohr effect (Delta logP(50)/ Delta logpH=-0.45). The phosphate binding curve allowed to measure a very high overall binding constant (K= 1.18 x 10(5) 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 alpha(1)/beta(1) and alpha(1)/beta(2) interfaces, such as alpha 38 and alpha 89 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. (C) 2007 Elsevier Inc. All rights reserved.