Heme peroxidases are oxidative metabolizing enzymes ubiquitously distributed in plants, animal tissues, and micro-organisms and oxidize a broad range of substrates by utilizing hydrogen peroxide (H 2 O 2 ) as an oxidant (1, 2). The substrates are oxidized by two common intermediates of heme peroxidases called compounds I and II. Compound I is formed upon the activation of H 2 O 2 with the resting enzymes and contains an oxyferryl porphyrin -cation radical (3). Compound I oxidizes the substrate and converts to compound II containing an oxyferryl heme, which returns to the resting state by oxidizing another molecule of the substrate. Heme peroxidases develop an efficient mechanism to capture and activate H 2 O 2 rapidly and specifically. The bimolecular rate constant for the formation of compound I (1.7 ϫ 10 7 M Ϫ1 s Ϫ1

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