ADAPTATION TO EXTREME ENVIRONMENTS - STRUCTURE-FUNCTION-RELATIONSHIPS IN EMPEROR PENGUIN HEMOGLOBIN

The functional properties of the single haemoglobin (Hb) of Emperor penguin (Aptenodytes forsteri) have been investiganted at different temperatures as a function of proton and organic phosphante concentration. The complete amino acid sequence has been established. Comparison with that of human HbA shows 12 substitutions in the contact regions of αβ dimers. In addition to overall similarities shanred with most of the avian Hbs previously described, this Hb shows significant differences, which could be related to the peculiar behaviour of this penguin. In particular we may consider that: (1) the shape of the Bohr effect curve seems well adapted for gas exchange during very prolonged dives, preserving penguin Hb from a sudden and not controlled stripping of oxygen; (2) the very minor enthalpy change observed at lower pH could be an example of molecular adaptation, through which oxygen delivery becomes essentially insensitive to exposure to the extremely low temperatures of the environment. Moreover, the smanll alkaline Bohr effect has been found to be only chloride-linked, since the pH dependence of the oxygen affinity is totally abolished in the absence of this ion. These functional characteristics are discussed on the basis of the primary structure of α and β-chains. © 1994 Academic Press, Inc.