Pseudo cross-link of human hemoglobin with mono-(3,5-dibromosalicyl)fumarate

The reaction of human oxyhemoglobin with mono-(3,5-dibromosalicyl)fumarate, produces a derivative specifically acylated at the two lysines β82, which can be purified with a 70% yield. The oxygen affinity of this derivative at 37°C at pH 7.4, 0.1 M Cl^- is of 12 mm Hg, and is not affected by organic phosphate. In the presence of 5% CO₂, the oxygen affinity decreases to 25 mm Hg. In all cases the cooperativity is lowered, with a value of n in the Hill plots near 2. Sedimentation velocity measurements indicate that, contrary to normal hemoglobin, this derivative fails to dissociate into dimers upon exposure to pH 5.5. The stability of the tetrameric structure is probably due to a modification of the β-β interface, resulting from electrostatic and hydrophobic interactions introduced in the β cleft by the fumaryl residues. These new interactions are probably the origin of a new reverse Bohr effect group at alkaline pH. Consistent with the stabilization of the tetrameric structure, the half-time of retention of this compound in the rat is increased 4-fold with respect to that of normal hemoglobin. These characteristics cast a favorable light on the usage of this compound as an oxygen carrier in transfusional and perfusional fluids.