Haemoglobin (Hb), a well studied globular protein, transports oxygen from the heart to different parts of the body. The physiological function of haemoglobin as an oxygen carrier was first Linifanib AL-39324 demonstrated by Pfluger in 1875. The three-dimensional structure of haemoglobin is held together by hydrogen bonds, salt bridges and weak noncovalent interactions. Haemoglobin is considered to be an allosteric molecule with oxygen acting as a substrate and protons, chloride ion and organic phosphates acting as allosteric

effectors. The oxygen affinity of haemoglobin is expressed by the partial pressure (P) of oxygen at which haemoglobin is saturated. In birds, the respiratory system is formed by small air sacs that serve as tidal ventilation for the lungs and have no significant exchange across their cells. The respiratory tract forms a large portion of the total oxygen-storage capacity of the

body in birds, whereas in mammals the respiratory-tract oxygen forms a much smaller proportion of the total oxygen storage of the body. Birds are almost unique in their ability to fly, which is a highly energy-consuming form of locomotion. The respiratory system of birds differs from that of mammals by uniquely adapting to very high oxygen consumption during flight. The ability of birds to maintain an efficient oxygen supply to the brain during severe hypoxia is an important adaptation contributing to their exceptional tolerance of extreme altitudes. Compared with mammalian Hb, the presence of hydrophobic residues is increased in avian Hb, which leads to its higher thermal stability and consistent attainment of the tense (T) state (Ajloo et al., 2002 ). The conservation of hydrophobic domains in avian Hbs might in fact have been required for the stabilization of tertiary structure in order to maintain the

function of the protein through a long period of evolution (Perutz, 1983 ). The great cormorant (Phalacrocorax carbo), known as the larger cormorant in India, can be observed fishing even deep underwater and can also fly at high altitude. In general, birds that fly at high altitudes have lower P 50 values; for example, Ruppell’s griffon vulture can fly up to 11 000 m (P 50 = 2.1 kPa), European black Drug_discovery vultures fly at about 4500 m (P 50 = 2.8 kPa) and bar-headed geese can fly up to 8000 m (P 50 = 3.6 kPa) above sea level. Cormorant haemoglobin shares nearly 95% sequence similarity with those from Ruppell’s griffon vulture, European black vulture, greylag goose (Liang et al., 2001 ) and bar-headed goose (Zhang et al., 1996 ). This shows that the cormorant has retained most of the conserved amino-acid residues (Huber et al., 1988 ) that help to provide oxygen affinity even at high altitudes. The cormorant can fly at high altitude at a maximum speed of 45.72 km h−1 and it can also dive deep into the water to fish even at 30.5–36.6 m.