l-Dopa peroxidase activity of human erythrocyte catalase

The human red cell hemolysate was found to have 3-(3′,4′-dihydroxyphenyl)-l-alanine (l-dopa) peroxidase activity. During the purification of glutathione peroxidase and catalase by ammonium sulfate precipitation, ion exchange chromatography, Sephadex gel filtration, and preparative polyacrylamide disc electrophoresis, the l-dopa peroxidase activity was found to be associated with catalase. Both sodium azide, 8 mM, and 3-amino-1,2,4-triazole, 50 mM, besides inhibiting catalase, inhibited the l-dopa peroxidase activity in each fraction. Ethylenediamine tetraacetic acid (EDTA), 4 mM, had no effect on catalase or l-dopa peroxidase activity, indicating that the oxidation of l-dopa is not a nonenzymatic process mediated by metal ions. Although the electrophoretic mobility of catalase, l-dopa peroxidase, and glutathione peroxidase are similar, a homogeneous preparation of glutathione peroxidase was free of l-dopa peroxidase activity. l-Dopa peroxidase in human red cells was co-purified with catalase.