Polymerization of Recombinant Hemoglobin F yE6V and Hemoglobin F yE6V, yQ87T Alone, and in Mixtures With Hemoglobin S

To further understand determinants for Hemoglobin (Hb) S polymerization, as well as the inhibitory mechanism of Hb F on Hb S polymerization, Hb F variants containing Val-* (Hb F yE6V) or Val-*, Thr-y87 (Hb F yE6V. yQ87Tj were expressed in yeast. The oxy form of Hb F yE6V was about 10-fold less stable to mechanical agitation than native oxy Hb F, which is similar to stability differences comparing oxy Hb S and oxy Hb A. Deoxy Hb F yE6V showed -20-fold decreased solubility compared with native deoxy Hb F in high phosphate buffer and formed gels like deoxy Hb S in low phosphate buffer, indicating thatthe Val-@substitution decreases solubility of Hb F like Val-pG in deoxy Hb S. Oversaturated deoxy Hb F yE6V polymerized without a delay time in low and high phosphate buffers, in contrast to deoxy Hb S, which is accompanied by a distinct delay time before polymerization. Deoxy Hb F yESV, yQ87T also polymerized without a delay time like deoxy Hb F yE6V. These results suggest that deoxy Hb F yE6VyQ87T polymers are different from those of deoxy Hb S, and that contact sites differ from those of deoxy Hb S, even though both have the same primary donor (A31 and acceptor sites in the EF helix. These results also suggest that other amino acids in addition to