Polymerization of hemoglobin S: Quinary interactions of Glu-43(β)

Hemoglobin S (HbS) Hoshida and three substituted forms of HbS Hoshida (the substituents being on the amide nitrogen of Gln-43(β)) have been prepared by the amidation of Glu-43(β) of HbS with ammonia, methylamine, glycine ethyl ester, and galactosamine. The O₂ affinity of HbS is increased slightly on amidation of Glu-43(β). All the four amidated derivatives exhibited nearly the same oxygen affinity. On the other hand, the influence of amidation on the solubility exhibits some sensitivity to the chemical nature of the substituent on the Gln-43(β). The solubility of HbS Hoshida (a case with no substitution on Gln-43(β)), and the methyl-substituted derivatives are about 33 and 36% higher than that of HbS. The solubility of the HbS modified with the glycine ethyl ester or galactosamine is increased to 41 and 47%, respectively. The first derivative UV spectra of HbS Hoshida and its methyl derivative reflect very little perturbations in their α₁β₂ interface as compared with that of HbS, whereas the amidated derivatives with larger substituents on Gln-43(β) reflected noticeable differences. Thus, the increase in the solubility and the oxygen affinity of HbS on the amidation of Glu-43(β) is primarily a consequence of the loss of the negative charge at 43(β), a residue proximal to the α₁β₂ interface. The copolymerization studies of amidated HbS with HbA, and HbS with amidated HbA demonstrate that cis Glu-43(β) is the "active" residue. This assignment is discrepant with the earlier implication of a trans configuration for this residue in the polymer (Edelstein, S. J. (1981) J. Mol. Biol. 150, 557-575). However, it is consistent with the solution studies of Nagel et al. (Nagel, R. L., Bookchin, R. M., Johnson, J., Labie, D., Wajcman, H., Isaac-Sodeye, W. A., Honig, G. R., Schiliro, G., Crookstan, J. H., and Matsutomo, K. (1979) Proc. Nat. Acad. Sci. U. S. A. 76, 670-672) and McCurdy et al. (McCurdy, P. R., Lorkin, P. A., Casey, R., Lehmann, H., Uddin, D. E., and Dickson, L. G. (1974) Am. J. Med. 57, 665-760).