Polymerization of carbamylated deoxyhemoglobin S in concentrated phosphate buffer

To study the effect of carbamylation on the polymerization of deoxyhemoglobin (HB) S, three types of NH2-terminal-carbamylated Hb S specifically modified at the NH2 termini at the alpha, beta, or all four subunit chains, alpha c2 beta sc2, and alpha 2 beta sc2, and epsilon-lysine-carbamylated Hb S were prepared by reacting Hb S with cyanate. The solubility of deoxy-Hb S in concentrated phosphate buffer was increased by carbamylation of the NH2-terminal residues of beta chains. Kinetic studies on the polymerization of purified carbamylated deoxy-Hb S showed that the length of the delay time prior to polymerization is related to solubility; carbamylated Hb S with higher solubilities exhibited longer delay times than those with lower solubilities. The delay times for alpha 2 beta sc2 and alpha c2 beta sc2 were prolonged 2-3- and 3-6-fold, respectively, as compared to those of native deoxy-Hb S in 1.8 M phosphate buffer. The logarithmic plot of reciprocal delay time versus hemoglobin concentration of alpha c2 beta s2, alpha 2 beta sc2, and epsilon-lysine-carbamylated deoxy-Hb S showed straight lines with slopes (n values) of 4.0, 3.8, 3.6, and 3.5, respectively. These values are slightly higher than the n value of native deoxy-Hb S (n = 2.7), suggesting that nuclei of carbamylated Hb S are larger than those of native deoxy-Hb S.