Alkaline Bohr effect of bird hemoglobins: the case of the flamingo

The hemoglobin (Hb) substitution His→Gln at position α89, very common in avian Hbs, is considered to be responsible for the weak Bohr effect of avian Hbs. Phoenicopterus ruber ruber is one of the few avian Hbs that possesses His at α89, but it has not been functionally characterized yet. In the present study the Hb system of the greater flamingo (P. ruber roseus), a bird that lives in Mediterranean areas, has been investigated to obtain further insight into the role played by the α89 residue in determining the strong reduction of the Bohr effect. Functional analysis of the two purified Hb components (HbA and HbD) of P. ruber roseus showed that both are characterized by high oxygen affinity in the absence of organic phosphates, a strong modulating effect of inositol hexaphosphate, and a reduced Bohr effect. Indeed, in spite of the close phylogenetic relationship between the two flamingo species, structural analysis based on tandem mass spectrometry of the αA chain of P. ruber roseus Hb showed that a Gln residue is present at position α89.