MOLECULAR BASIC OF RESPIRATION IN BIRDS: PRIMARY STRUCTURE OF HEMOGLOBIN FROM TUFTED DUCK (AYTHYA FULIGULA, NASRIFORMES)

The primary structure of aA-,aD-and B-chains from the hemoglobin of Tufted duck (Aythya fuligula) has been elucidated. Tufted duck belongs to the avian order Anseriformes, family Anatidae. This order includes aquatic birds like ducks, geese and swans commonly known as waterfowl. Members of this order are well known for their exceptional tolerance to hypoxia.Separation of the polypeptide subunits was achieved by ion exchange chromatography. The globin chains were degraded by enzymatic and chemical cleavages into peptides. The primary structure of hemoglobin was established by sequence determination of native chains and its tryptic and hydrolytic peptides by automatic Edman degradation in a Gas-phase sequencer.The hemoglobin of Tufted duck is heterogeneouos, having two hemoglobin components, like all other Anseriformes representatives. Positions aA13 Ile, aA99 Arg, aA135 Thr, aD120 Asp, B10 and B11 Ile are specific to Tufted duck hemoglobin. Alignment of the primary structure with Anserformes representatives indicates a high degree of homology within the order. Homologous comparison with other avian species reveals much conservation in the B-chain as compared to aA –and aD-chain. The automated homology model building was performed using the protein structure modeling package, WHAT IF. The three dimensional models of the two components i.e. HbA and HbD were calculated using crystal structure coordinates of Bar-headed goose (PDB id=A4F) and Chicken (PDB id=I hbr) hemoglobin. The various exchanges at positions critical for structure and function of the hemoglobin are discussed.