Chemically modified and recombinant hemoglobin blood substitutes

Modulation of reactivity and conformation within the T-quaternary state of human hemoglobin: the combined use of mutagenesis and sol-gel encapsulation

A range of conformationally distinct functional states within the T quaternary state of hemoglobin are accessed and probed using a combination of mutagenesis and sol-gel encapsulation that greatly slow or eliminate the T --> R transition. Visible and UV resonance Raman spectroscopy are used to probe the proximal strain at the heme and the status of the alpha(1)beta(2) interface, respectively, whereas CO geminate and bimolecular recombination traces in conjunction with MEM (maximum entropy method) analysis of kinetic populations are used to identify functionally distinct T-state populations. The mutants used in this study are Hb(Nbeta102A) and the alpha99-alpha99 cross-linked derivative of Hb(Wbeta37E). The former mutant, which binds oxygen noncooperatively with very low affinity, is used to access low-affinity ligated T-state conformations, whereas the latter mutant is used to access the high-affinity end of the distribution of T-state conformations. A pattern emerges within the T state in which ligand reactivity increases as both the proximal strain and the alpha(1)beta(2) interface interactions are progressively lessened after ligand binding to the deoxy T-state species. The ligation and effector-dependent interplay between the heme environment and the stability of the Trp beta37 cluster in the hinge region of the alpha(1)beta(2) interface appears to determine the distribution of the ligated T-state species generated upon ligand binding. A qualitative model is presented, suggesting that different T quaternary structures modulate the stability of different alphabeta dimer conformations within the tetramer.

Prolongation of the intravascular retention of hemoglobin modified with a long-chain fatty acid derivative

To develop hemoglobin (Hb) derivatives with an increased circulatory half-life, Hb was chemically modified with long chain fatty acid analogs. One compound, sodium 1-hexadecyl 6-(2-iodoacetamido)hexyl phosphate, specifically modified the Cys-93 beta residues of human hemoglobin (HbA) as determined by sulfhydryl titration analysis. The resulting modified Hb derivative, FAHbA, was isolated and was shown to have a two-fold longer circulatory half-life than native HbA in a rat low-dose acute transfusion model.