Interaction of haemoglobin with dextran sulphates and the oxygen-binding properties of the covalent conjugates

Abstract

The interactions between dextran sulphates of various molecular weights with both oxy- and deoxyhaemoglobin were studied by a potentiometric method and by measurement of their oxygen-binding parameters. These polyanionic polymers were shown to act as macromolecular effectors: in fact they bind to the liganded haemoglobin by means of a large number of relatively weak sites, whereas they strongly bind to the unliganded protein by means of a tight interaction inside the diphosphoglycerate binding cavity, which allowed the determination of the average binding stoichiometries of the dextran sulphate-deoxyhaemoglobin complexes. In both cases, the higher the molecular weight of dextran sulphate, the weaker the interaction, probably because of the steric hindrance, which hampers the approach of the protein by the polymer. In the light of these results, the conditions of the covalent fixation of dextran sulphate onto haemoglobin were defined, in order to obtain covalent conjugates with low oxygen affinity.