Hemoglobin-dialdehyde dextran conjugates: improvement of their oxygen-binding properties with anionic groups.

We studied the conjugates formed between hemoglobin and sulfated or unsulfated oxidized dextran. It appears that the presence of sulfated groups favors imino bond formation between the protein and the polymer, as the average molecular size of the conjugates is larger in this case. Under neutral conditions, the oxygen-binding properties of the conjugates depend on the presence or absence of oxygen during the coupling reaction. With unsulfated dextran, oxyhemoglobin leads to conjugates with increased oxygen affinity (P50/P50 native hemoglobin approximately 0.5) compared to that of free hemoglobin (P50 = 4 mm Hg), whereas deoxyhemoglobin leads to conjugates with decreased oxygen affinity (P50/P50 native hemoglobin approximately 3). The use of sulfated dextran reinforces this lowering in oxygen affinity, which indicates that sulfated dextran acts as a permanent macromolecular effector of hemoglobin (P50/P50 native hemoglobin approximately 4). Moreover, it can be assumed that some of the linkages involve the 2,3-diphosphoglycerate binding site, as the strong effector inositol hexaphosphate has only a slight effect on the oxygen-binding properties of the conjugate prepared in the deoxy state (P50/P50 native hemoglobin close to 4.4 and 6, respectively, for unsulfated and sulfated conjugates). Although dextran substituted with benzenehexacarboxylic acid (BHC) leads to a low-oxygen-affinity conjugate when linked to oxyhemoglobin through amide bonds (P50/P50 native hemoglobin approximately 5), oxidized dextran modified with BHC leads, with oxyhemoglobin, to a conjugate whose oxygen affinity is close to that of free hemoglobin (P50/P50 native hemoglobin approximately 1.2).