Catalase-peroxidase from Synechocystis is capable of chlorination and bromination reactions

Catalase-peroxidases (KatGs) are multifunctional heme peroxidases exhibitin g an overwhelming catalase activity and a substantial peroxidase activity o f broad specificity. Here, we show that catalase-peroxidases are also halop eroxidases capable of oxidizing chloride, bromide, and iodide in a peroxide -and enzyme-dependent manner. Recombinant KatG and the variants R119A, W122 F, and W122A from the cyanobacterium Synechocystis PCC 6803 have been teste d for their halogenation activity. Halogenation of monochlorodimedon (MCD), formation of triiodide and tribromide, and bromide- and chloride-mediated oxidation of glutathione have been tested. Halogenation of MCD by chloride, bromide, and iodide was shown to be catalyzed by wild-type KatG and the va riant R119A. Generally, rates of halogenation increased in the order Cl- < Br- < I- and/or by decreasing pH. The halogenation activity of R119A was ab out 7-9% that of the wild-type enzyme. Upon exchange of the distal Trp122 b y Phe and Ala, both the catalase and halogenation activities were lost but the overall peroxidase activity was increased. The findings suggest that th e same redox intermediate is involved in H2O2 and halide oxidation and that distal Trp122 is involved in both two-electron reactions. That halides com pete with H2O2, for the same redox intermediate is also emphasized by the f act that the polarographically measured catalase activity is influenced by halides, with bromide being more effective than chloride. (C) 2001 Academic Press.