On Dissociation and Recombination of Human Adult Hemoglobins A, S, and C.

According to experiments reported by Field and O'Brien,I acidification of normal human adult hemoglobin (Hb A) from pH 6 to pH 3.5 is accompanied by a progressive, reversible decrease in sedimentation constant, together with an increase in translational diffusion constant. These findings were interpreted as showing the presence of a rapidly reversible, hydrogen-ion-dependent dissociation of Hb A into half-molecules. Vinograd,' using the more direct Archibald method of molecular weight determination,3 has confirmed these results. It occurred to us that if other human hemoglobins also undergo reversible dissociation, "hybrid" molecules of hemoglobin might be formed by dissociation and reassociation of the subunits in a mixture of two different types of hemoglobin. Our studies have dealt with Hb A and the abnormal adult forms, S (sickle cell) and C.', 5 Their comparative ultracentrifugal properties at different acid pH were found to be indistinguishable, indicating that the three types of hemoglobin are equally susceptible to reversible acid dissociation. Mixtures containing the three possible pairs of these types were acidified and neutralized. The sedimentation behavior of the neutralized samples showed that reassociation had occurred; however, electrophoretic analyses gave no indication of the presence of hybrid molecules.