O₂ binding and dissociation and ligand exchange reaction of O₂ with CO in polymer composite films of hemoglobin

A polymer composite film of hemoglobin (Hb-polymer film) was prepared by the casting of an Hb-polymer mixed solution (weight ratio of Hb to polymer is 1 to 1). The percentages of O₂ and CO saturation of the Hb-dextran film were 46% and 70%, respectively. In the Hb solution, 100% saturation was observed for both Hgands, and a humidified Hb-dextran film also showed 100% saturation. Water molecules would provide flexibility to the matrix polymer and promote a structural change in the Hb from a tense state (T) to a relaxed state (R). Thus the ligand binding to the Hb in the polymer films was strongly affected by the degree of interaction of Hb with the matrix polymers and the physical properties of the polymers. Inositol hexaphosphate (IHP) worked as an allosteric effector even in the solid polymer film and lowered the oxygen affinity of Hb. The O₂ transport through an Hb-polyethyleneimine (PEI) film with IHP showed the facilitated O₂ transport in comparison with the film without IHP because of the high dissociation rate of O₂ from Hb with IHP.