| Abstract
| - The structural and energetic properties of the compound II intermediate in the catalytic reaction of peroxidasesand catalases are compared in order to investigate why catalases, unlike peroxidases, rarely form compoundII. Our calculations, based on the density functional theory (DFT)/Car−Parrinello molecular dynamicsmethodology (CPMD), show that catalase compound II is a stable intermediate with respect to liganddissociation, with Fe−ligand binding energies comparable to those found for other hemeproteins such asmyoglobin and cytochrome c. Nevertheless, catalase shows much weaker iron−ligand bonds compared tothose of peroxidase, which is due to the opposite effect of the proximal hydrogen-bonded residues (Arg+ incatalase and Asp- in peroxidase). Comparison with the available structural information suggests that, contraryto the often assumed oxoferryl bond of compound II, some of the reported structures might instead correspondto a hydroxyferryl bond. Some hints on the role of the proximal hydrogen-bonded residues in modulating thestability of the different species during the catalytic reaction are provided.
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