EFFECT OF COVALENT LABELING OF DEXTRAN-BENZENEHEXACARBOXYLATE ON HEMOGLOBIN

The covalent fixation of benzenehexacarboxylate (BHC) onto dextran was carried out according to several reaction schemes, The polvanionic po lymers thus synthesized were capable of decreasing the oxygen affinity of hemoglobin by specifically interacting with the 2,3-diphosphoglyce rate (2,3-DPG) binding site of the protein. The intensity of this effe ct was correlated to both the chemical structure of the polyanionic po lymers and the BHC content in polymer. The polvanionic polymer, contai ning 0.035 mol BHC/g and presenting no cross-linking between its polym er chains, possessed the best effector properties. These properties we re used to direct the covalent fixation of the dextran-benzenehexacarb oxylate onto the phosphate binding site of the protein. The resulting hemoglobin was mainly substituted at the same time by one or more link ed BHC onto both alphabeta dimers in the vicinity of the 2,3-DPG site. Thus, the modification of hemoglobin led to an increase in the hydrod ynamic volume of each dimer sufficient to limit the diffusion of the c onjugates through the kidney membrane, even if the conjugates had diss ociated into alphabeta dimers. Compared to that of free hemoglobin, th e oxygen affinity of the conjugates was significantly decreased. This type of covalent conjugate exhibited general properties quite suitable for use as blood substitutes.