Hemoglobin Autoxidation at Physiological Concentrations

Methemoglobin formation was studied at near physiological hemoglobin concentration. The reaction proceeds at a faster rate when the concentration of hemoglobin is high (15-18 mM in heme) than when it is low (2 mM). Constant shaking of hemoglobin preparations during the incubation decreases the differences seen in the rates of autoxidation between concentrated and dilute samples. When red cell hemolysate is used instead of pure hemoglobin, similar results are obtained. A comparison of rates of methemoglobin formation in hemoglobin solutions under low air pressure (1/2 atm) with those under normal air pressure (1 atm) shows no differences between concentrated and dilute samples. There is also no significant difference between the rates of autoxidation of dilute and concentrated solutions when the reactions are carried out under one atmosphere of oxygen (100 percent O2). The study of one patient with hereditary spherocytosis demonstrated higher hemoglobin autoxidation rate in spherocytes, which have higher hemoglobin concentration, than in normal biconcave red cells. These results suggest that: a) the rate of hemoglobin autoxidation at red cell hemoglobin concentration is significantly faster than rates obtained by studying dilute solutions; b) although the accelerated oxidation might be related to multiple factors, one seems to be less accessibility of oxygen when the hemoglobin solution is highly concentrated.