HEMOGLOBIN-DIALDEHYDE DEXTRAN CONJUGATES - IMPROVEMENT OF THEIR OXYGEN-BINDING PROPERTIES WITH ANIONIC GROUPS

We studied the conjugates formed between hemoglobin and sulfated or un sulfated oxidized dextran. It appears that the presence of sulfated gr oups 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 conju gates depend on the presence or absence of oxygen during the coupling reaction. With unsulfated dextran. oxyhemoglobin leads to conjugates w ith increased oxygen affinity (P-50/P-50 native hemoglobin approximate to 0.5) compared to that of free hemoglobin (P-50 = 4 mm Hg), whereas deoxyhemoglobin leads to conjugates with decreased oxygen affinity (P ,,IP,, native hemoglobin approximate to 3). The use of sulfated dextra n reinforces this lowering in oxygen affinity, which indicates that su lfated dextran acts as a permanent macromolecular effector of hemoglob in (P-50/P-50 native hemoglobin approximate to 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 prepa red in the deoxy state (P-50/P-50 native hemoglobin close to 4.4 and 6 , respectively, for unsulfated and sulfated conjugates). Although dext ran substituted with benzenehexacarboxylic acid (BHC) leads to a low-o xygen-affinity conjugate when linked to oxyhemoglobin through amide bo nds (P-50/P-50 native hemoglobin approximate to 5), oxidized dextran m odified with HC leads, with oxyhemoglobin, to a conjugate whose oxygen affinity is close to that of free hemoglobin (P-50/P-50 native hemogl obin approximate to 1.2).