Calorimetric studies of oxyhemoglobin ligand dissociation. III. Evidence for a hemoglobin-catalase-superoxide dismutase integrated system in the oxygen depletion by dithionite.
Calorimetric studies of the effect of superoxide dismutase and/or catalase on the reduction of dioxygen into water by dithionite in oxyhemoglobin have been carried out and the results compared with those in red cell hemolysates. In the absence of the enzymes the stoichiometry (moles dithionite/mole dioxygen) is less than the value of 2:1 which was found previously in red cell hemolysates [Forlani et al., J. Inorg. Biochem. 20, 147-155 (1984)]. In the presence of either superoxide dismutase or catalase alone the stoichiometry increases but is still less than 2:1. In the presence of both enzymes the stoichiometry and the shape of the thermogram is that previously observed for hemolysates, suggesting the presence of a hemoglobin-catalase-superoxide dismutase integrated system. The absence of a calorimetric signal for hydrogen peroxide in the reduction of oxyhemoglobin in the presence of superoxide dismutase suggests a wider biological role of superoxide dismutase than previously thought.