Gelation equilibrium concentrations (C_sat ) of recombinant HbS mutants. The C_sat is given in milligrams per milliliter. All measurements were performed in the presence of dextran in 50 mmol/L potassium phosphate buffer, pH 7.5, at 37°C, as described in the text. (1) HbS; (2) double HbS mutant E6V(β)/E121R(β); (3) triple HbS mutant D75Y(α)/E6V(β)/E121R(β); and (4) quadruple HbS mutant D6A(α)/D75Y(α)/E6V(β)/E121R(β).