Bis[2-(4-carboxyphenoxy)carbonylethyl]phosphinic acid (BCCEP): a new reagent for hemoglobin modification

The synthesis and hemoglobin cross-linking studies of a novel organic reagent, bis[2-(4-carboxyphenoxy)carbonylethyl]phosphinic acid (BCCEP; 2) has been reported. The reagent was synthesized in four steps from hydroxybenzoic acid. The tri-sodium salt of BCCEP was employed to cross-link oxyHb, and the product was purified by DEAE-cellulose chromatography. The purified material was analyzed by SDS-PAGE, IEF, and HPLC analyses, which clearly showed the formation of covalent, intramolecular cross-links. While SDS-PAGE analyses of individual bands pointed to the molecular weight range of 32 kDa, the HPLC analyses suggested that the cross-links had formed between beta 1-beta 2 subunits. The oxygen equilibrium measurements and the Hill plots were performed on the purified bands to assess oxygen affinity as well as cooperativity of oxygen binding of the modified hemoglobins. All bands corresponding to modified hemoglobins showed significantly reduced oxygen affinity as compared with that of cell-free hemoglobin, as desired. The modified hemoglobins, however, exhibited somewhat reduced oxygen-binding cooperativity as contrasted with human stroma-free hemoglobin. Molecular dynamics simulation studies (Insight II/Discover/Biosym) on the Reagent-HbA0 complex suggested that the most likely amino acid residues involved in the cross-linking are Lys82 or N-terminal Val1 on one of the beta chains, and Lys144 on the other.