Oxygen Equilibria of Hemoglobin A2 and Hemoglobin

Human hemoglobin provides a model for studies concerned with the relationships of structure and biologic function of proteins. Older evidence for conformational differences between oxygenated and deoxygenated normal hemoglobin (1) has recently been confirmed and extended by X-ray crystallographic studies (2) and by comparison of the dissociation (3) and of the hybridization (4) of the oxygenated and deoxygenated pigments. Normal and abnormal human hemoglobins have been utilized in the past by other workers for in-vestigation of relationships between structure and oxygen equilibria. Some of these observations, grouped on the basis of the structure of the he-moglobins studied, are briefly cited below. 1) Normal human, hemoglobins A (aA p2A), F (a,2A 'F), and A. (a2A 8A-) are tetramers con-taining apparently identical aA polypeptide chains, but differing in the non-alpha chains. Extensive studies of the oxygen equilibria of hemolysates pre-pared from the erythrocytes of normal subjects and of normal erythrocytes, containing almost entirely hemoglobin A, provide values with which data on other human hemoglobins may be com-pared. The increased oxygen affinity observed in the whole blood of newborn infants (5, 6) can-not be due solely to the presence of hemoglobin F, since solutions of hemoglobin F and of hemo-globin A exhibit the same oxygen dissociation curves (7, 8). Furthermore, in the studies o