Polymerization of binary mixtures of hemoglobin S and carbamylated hemoglobin S

To study the mode of interaction between hemoglobin (Hb) S and carbamylated Hb S, the kinetics of polymerization of various mixtures of deoxy-Hb S and NH2 termini carbamylated Hb S in concentrated phosphate buffer was determined. These mixtures were found to polymerize with a clear demonstration of a delay time as does each hemoglobin in its pure form. Both the delay and the polymerization times were prolonged as the fraction of carbamylated Hb S was increased. Electrophoretic analysis of the polymer fraction showed that the amount of carbamylated Hb S increased linearly in the polymer phase with increases in the fraction of carbamylated Hb S in the starting mixture. The ratio of Hb S to carbamylated Hb S in the polymer phase was slightly higher than that in the initial solution mixture, suggesting that Hb S polymerizes more easily than carbamylated Hb S. To examine the role of hybrid hemoglobin in the binary mixtures of carbamylated Hb S and Hb S, we compared the rate of polymerization under which hybrid formation may be prevented or allowed to take place. It was found that the rate of polymerization for the mixtures of carbamylated Hb S and Hb S mixed in the oxy state did not differ from that mixed in the deoxy state. In addition, polymerization occurred even when the critical concentration of each component in the mixture was lower than that of either pure Hb S or pure carbamylated Hb S. These results suggest that all hemoglobin species can participate in the nucleation and polymerization steps of mixtures of carbamylated Hb S and Hb S.