Peroxidase activity of oxyhaemoglobin in vitro

In bovine erythrocyte suspensions incubated with 16 mM aniline, 4-phenetidine, 4-chloro- or 3,4-dichloroaniline for three hours at 37 degrees C, HbFe3+ concentrations of 10, 35, 77 and 93%, respectively, were found. N- and C-oxygenation products of aniline, 4-chloro-, and 3,4-dichloroaniline were formed, which can explain the oxidation of HbFe3+, indicative of peroxygenase activity of oxyhaemoglobin. The same N- and C-oxygenated derivatives of 4-chloro- and 3,4-dichloroaniline were also formed by hepatic microsomes, although at a 25- to 5000-fold higher rate. HbFe3+ was formed more readily on incubation of either bovine erythrocytes or purified human Hb with various N-arylacetohydroxamic acids. The metabolites of N-(4-chlorophenyl)-N-hydroxyacetamide are the same as the products of chemical oxidation of NOH-4ClAA by PbO2 or KMnO4, indicating the peroxidase activity of oxyhaemoglobin.