Concerted formation of the gel of hemoglobin S.

Apparent weight-average molecular weights of hemoglobin A and hemoglobin S were measured at high concentrations by equilibrium ultracentrifugation. Carbonmonoxy-hemoglobin S appears to exist as a solution of unassociated molecules, as do carbonmonoxy-and deoxy-hemoglobin A. Deoxy-hemoglobin S, however, exists in a gel-like state at concentrations above 14 g/dl, but no aggregates smaller than the gel were observed in solutions that were in equilibrium with the gel. Carbamoylation of hemoglobin S produced a solution of unaggregated molecules, as did cooling of uncarbamoylated hemoglobin S to 5 degrees . It is concluded that the gel of hemoglobin S is formed in a stoichiometrically concerted manner, and that the size of the smallest stable aggregate is greater than 20 hemoglobin molecules.