Functional Switching of Amphitrite ornata Dehaloperoxidase from O2-Binding Globin to Peroxidase Enzyme Facilitated by Halophenol Substrate and H2O2

Abstract

Amphitrite ornata dehaloperoxidase (DHP) is the first heme-containing globin possessing a native peroxidase enzymatic activity. DHP catalyzes the H(2)O(2)-dependent dehalogenation of halophenols. By possessing this detoxifying enzymatic activity, these organisms are able to thrive in an environment contaminated with toxic haloaromatics. It has been proposed that DHP evolved from a dioxygen carrier globin protein and therefore possesses dual physiological roles of O(2) carrier and dehaloperoxidase. Although DHP is isolated in the catalytically inactive oxyferrous state (oxy-DHP), we find that the combination of H(2)O(2) and the substrate 2,4,6-trichlorophenol (TCP) brings about facile switching of oxy-DHP to the enzymatically active ferric state via a process likely involving substrate radicals (TCP*). In contrast, in the absence of TCP, H(2)O(2) alone converts oxy-DHP to an inactive state (compound RH) instead of oxidizing the enzyme to the ferric state. Further, although the rate of autoxidation of oxy-DHP is somewhat enhanced by the presence of TCP, the effect is too small to be the functional switch. Instead, both substrate and H(2)O(2) are needed to convert oxy-DHP to the catalytically active ferric state. These observations provide a physiological link between the O(2) carrier role of the ferrous protein and the peroxidase activity of the ferric enzyme in this bifunctional protein.