Catalase catalytic cycles, scheme

During its catalytic cycle, the Mn catalases shuttle between the Mn and the Mn oxidation states in 2 two-electron reactions (137). Overall this process converts two hydrogen peroxide molecules into one molecule of dioxygen and two water molecules. A proposal for the catalytic cycle of catalase is presented in Scheme 8 (23). When the... 

This was followed by an article in 1997 (445), wherein Naruta et al. prepared a dimer with Mnwporphyrin(OMe)(OMe or OH). The analysis of this system indicated that catalase activity occurred via approach of hydrogen peroxide to the pocket of the dimer, followed by deprotonation and concomitant reduction of the dimer and oxidation of the hydrogen peroxide to dioxygen. Their proposed catalytic cycle is shown in Scheme 22. Similar systems have been used to generate dioxygen from water (discussed later). 

The oxidation of the iron(III) resting state of catalase by the first hydrogen peroxide molecule generates a high-valent metal-oxo species considered to be an iron(IV)-oxo with a radical-cation delocalized on the porphyrin ring, according to UV-visible, Raman, and EPR studies (see Scheme 4 for different intermediates of the catalytic cycle of catalase). ... 

The proposed catalase mechanism is depicted in Scheme 11.1. Hydrogen peroxide decomposition is initiated by (a) the binding of H2O2 to the Mn "-Mn " dinuclear center, and this is followed by (b) reduction to the Mn"-Mn" intermediate and concomitant oxidation of the peroxide to O2 [33, 34]. Subsequent binding of a second molecule of H2O2 to the Mn -Mn" species (c) is followed by the reduction of H2O2 to H2O and the oxidation of the Mn"-Mn" species (d), which closes the catalytic cycle [17]. 

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