Inhibition of hemoglobin S polymerization by N‐terminal band 3 peptides: New class of inhibitors: Solubility studies

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Abstract
Two synthetic peptides corresponding to the N‐terminal amino acids (AA) of band 3 were designed to inhibit deoxyhemoglobin S (deoxy S) polymerization through two different mechanisms. Peptide I, an N:1–15AA fragment, was employed to bind to the 2,3‐diphosphoglycerate (2,3‐DPG) receptor locus of single deoxy S molecules with 5–7 AA extending internally and the remaining 10‐8 AA projecting external to hemoglobin (Hb) S, thereby inhibiting polymerization by steric hindrance. Peptide II consisted of two N:1‐8AA + K (lysine) sequences linked by a coupler through the lysine, and it was employed to bind to the 2,3‐DPG loci of two deoxy S molecules, tethering them together to form “binary hemoglobin complexes” incapable of entering the polymer chains. Decreased polymerization would result from reduction in effective concentration of deoxy S. Binding of peptides to the 2,3‐DPG receptor loci was demonstrated by a progressive rightward shift in the hemoglobin oxygen binding curves as a function of increasing peptide concentrations. Inhibition of deoxy S polymerization was studied by equilibrium solubility measurements of purified, stripped solutions of Hb S. Physiologically significant inhibition was demonstrated for both peptides with near‐maximum increases in solubility achieved by Peptide II at 1:1 peptide:Hb S ratios. These peptides represent a new class of inhibitors of deoxy S polymerization.