High altitude and hemoglobin function in the vultures Gyps rueppellii and Aegypius monachus

Functional characteristics of the stripped composite hemoglobins (Hbs) of the vultures Gyps rueppellii and Aegypius monachus that can fly at extremely high altitudes, and of component Hbs of G. rueppellii are reported, in relation to influences of pH, temperature and inositol hexaphosphate. G. rueppellii Hbs A, A' and D represent a sequence of increasing oxygen affinity, which is opposite to earlier results on avian Hb components, but correlates with two alpha-chain substitutions that predictably affect oxygen affinity. The homo- and heterotropic interactions in oxygen binding are related to primary structures of the constituent polypeptide chains to trace molecular adaptations to high-altitude respiration, and to physiological factors (pulmonary hypoxia and hypocapnia, body temperature shifts, and lung and nasal gas and heat exchange) to discern their possible survival value at altitudes of 11,300 m.