Evidence of the incorporation of normally nonaggregating hemoglobins into crystalline aggregates of deoxy hemoglobin S.

Changes in the solubility of both components of binary mixtures of sickle-cell deoxyhemoglobin (Hb degrees S) and some normally nonaggregating hemoglobins were determined by direct compositional analysis of the solution phage following sedimentation of crystalline aggregates generated from them. Increases in turbidity associated with the suspension of the crystals in solution were also monitored for each mixture. Correlations between changes in species solubility and "excess' turbidity levels were observed which define two distinct forms of interaction between hemoglobin additives and Hb degrees S. The R-state quaternary structures, COHbS and metHbS in the absence of organic phosphate, are excluded from the aggregate phase and act to lower the solubility of Hb degrees S through increased excluded volume contributions to the activity of the solution phase. Increases in turbidity which parallel this solubility change reflect the increased population of highly asymmetric Hb degrees C crystals in solution. Deoxyhemoglobin A and metHbS fixed in the deoxy conformation lower the solubility of Hb degrees S in a more complex manner, which may include the establishment of a minimum solubility. The solubility of these additives also decreases, as does the turbidity due to the resultant crystals, when the proportion of additive exceeds 40% of the total. Analysis of the composition of pellets isolated from both hybrid and nonhybrid mixtures with Hb degrees A confirms its incorporation into the aggregates. Such "mixed" crystals appear to have solubility and morphological properties different from those of Hb degrees S alone. Comparison of phase composition data from mixtures prepared with varying initial concentrations of Hb degrees S suggests that the degree of HbA incorporation into HbS aggregates is a function of the amount of Hb degrees S itself available for self-aggregation and the stage of crystal development at which HbA participates.