Polycythemia associated with a hemoglobinopathy.

The efficiency of hemoglobin as an oxygencarrying substance is dependent upon certain features of its molecular configuration. The functional integrity of the molecule depends not only on spatial relationships between the heme and globin moieties, but on interrelations between the four globin chains (1, 2). The functional significance of portions of the molecule can be investigated by a study of hemoglobin with known abnormalities of structure. Many structural abnormalities have been reported, but functional abnormalities are extremely rare. Despite considerable differences in the amino acid composition of the fi, 8, and y chains, the oxygen dissociation curves of purified solutions of hemoglobin A (a2Ih8), hemoglobin F (ay,), and hemoglobin A2 (a282) are quite similar (3-5). In contrast, hemoglobins H (/4), Bart's (y,), and aA, in which interaction between a and , chains is impossible, have very high oxygen affinities (1, 2, 6). A Bohr effect is not present, and oxygen dissociation curves are hyperbolic rather than sigmoid in shape, indicating that heme-heme interac