Polymerization of AS hybrid hemoglobin. Potent inhibitory effect of hemoglobin A on the polymerization of AS hybrid hemoglobin.

Asymmetrically cross-linked AS hybrid hemoglobin (Hb AS-fumarate) was prepared by reacting a mixture of oxy-Hb A and oxy-Hb S with a cross-linking agent, bis(3,5-dibromosalicyl)fumarate. Kinetics of the polymerization of Hb AS-fumarate in 1.8 M phosphate buffer showed that Hb AS-fumarate polymerized similarly to Hb S-fumarate despite the presence of a beta A chain. The kinetics of the polymerization of a mixture of Hb AS-fumarate and Hb S-fumarate was similar to that of Hb S-fumarate or Hb AS-fumarate alone. However, when Hb AS-fumarate was mixed with Hb A, the delay time prior to polymerization of the mixture was markedly prolonged. Although the solubility of Hb AS-fumarate was similar to that of Hb S-fumarate, it nearly doubled upon the addition of Hb A. Analysis of Hb A in the polymer phase showed that a significant amount (35-40%) of Hb A copolymerized with Hb AS-fumarate. No such effect was observed when Hb A was mixed with Hb S-fumarate, where the delay time prior to polymerization and the solubility of the mixture were regulated by the concentration of Hb S-fumarate in the mixture. The strong inhibitory effect of Hb A on the polymerization of Hb AS hybrid hemoglobin may help explain the benign clinical course in sickle cell trait.