Polynitroxylated hemoglobin (Hb(AcTPO)12) has been developed as a hemoglobin-based oxygen carrier. While Hb(AcTPO)12 has been shown to exert beneficial effects in a number of models of oxidative injury, its peroxidase activity has not been characterized thus far. In the blood stream, Hb(AcTPO)12 undergoes reduction by ascorbate to its hydroxylamine form Hb(AcTPOH)12. Here we report that Hb(AcTPOH)12exhibits peroxidase activity where H2O2 is utilized for intramolecular oxidation of its TPOH residues to TPO. This represents an unusual redox-catalytic mechanism whereby reduction of H2O2 is achieved at the expense of reducing equivalents of ascorbate converted into those of Hb(AcTPOH)12, a new propensity that cannot be directly associated with ascorbate.
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