A stoichiometric study of heme degradation catalyzed by the reconstituted heme oxygenase system with special consideration of the production of hydrogen peroxide during the reaction.

In heme degradation catalyzed by the reconstituted heme oxygenase system, 8 to 9 mol of dioxygen and 11 to 12 mol of NADPH were consumed per mol of hemin lost, and about half the amount of dioxygen consumed could be accounted for by the production of hydrogen peroxide, which accumulated in the reaction mixture. Production of hydrogen peroxide in the heme oxygenase reaction did not appear to be due to the bimolecular dismutation of superoxide anions but rather seemed to be due to dissociation of a "peroxo" species formed on heme or intermediates of heme degradation. The hydrogen peroxide produced appeared to cause a considerable degree of non-specific degradation of heme (not leading to the formation of biliverdin) and also caused an inactivation of heme oxygenase. By taking into account the amount of dioxygen incorporated into hydrogen peroxide and some other factors, it could be deduced that 3 mol of dioxygen is consumed for the formation of 1 mol of biliverdin in the heme oxygenase reaction.