DIFFERENT FUNCTIONAL MODULATION BY HETEROTROPIC LIGANDS (2,3-DIPHOSPHOGLYCERATE AND CHLORIDES) OF THE TWO HAEMOGLOBINS FROM FALLOW-DEER (DAMA DAMA)

Two haemoglobin components have been identified and purified from fallow-deer (Dama dama) erythrocytes. They are present in similar amounts and the two tetrameric molecules share the same chain, while two different β chains are detected in the two components. The β chains differ by 14 residues, even though they both have 145 amino-acid residues, which account for a molecular mass of 16 023 and 16 064 Da, respectively, while chain has 141 residues, yielding a molecular mass of 15 142 Da. Compared with human Hb, the N-terminal region of both β chains shows deletion of Valβ1 and the replacement of Hisβ2 by a methionyl residue, a modification which is common to most ruminant haemoglobins. Although both isolated components show a low intrinsic affinity for oxygen, meaningful differences between the two haemoglobins have been found with respect to the effect of heterotropic effectors, such as 2,3-diphosphoglycerate and chloride ions. In view of the high sequence homology between the two components, the different effect of heterotropic ligands has been tentatively correlated to possible localized structural variations between β chains of the two haemoglobin components.