Band 3 peptides inhibit deoxy S polymerization: viscosity studies.

We have previously obtained evidence that N-terminal band 3 peptides inhibited deoxyhemoglobin S (deoxy S) polymerization as determined by equilibrium solubility assays. An N:1-15AA fragment binds to the 2,3-diphosphoglycerate (2,3-DPG) receptor locus of deoxy S with five to seven amino acids (AA) extending internally, while ten to eight AA remained external to deoxy S and inhibited polymerization by steric hindrance. A true mirror-image peptide, corresponding to two N:1-8AA + lysine (K) linked by coupler, binds to the 2,3-DPG loci of two deoxy S molecules, tethering them together to form "binary complexes" incapable of entering the polymer chains. The reduction in the concentration of deoxy S available for extended chain formation decreased polymerization. We now report time:viscosity profiles of the sol-gel transformation of purified solutions of deoxy S with and without peptides and studies of the gel solidity at equilibrium. Samples with peptides had longer lag times than controls of similar deoxy S concentrations. The mirror-image peptide was a more effective inhibitor than the N:1-15AA peptide. When the mirror-image peptide was present in peptide:hemoglobin molar ratios of 0.25-1:1, the increases in lag time were equivalent to decreasing the deoxy S concentrations by 15-25%, comparable to projected major therapeutic effects. Gel solidity, determined by yield temperature, was less in the sample with mirror-image peptide compared to control. These results support the proposed mechanisms of inhibition of deoxy S polymerization by band 3 peptides.