Among the family of catalytic heme iron enzymes,transient formation of oxidised?intermediates (Compounds I and II) is adefining feature of their mechanism.?Nature uses these Compound I and CompoundII intermediates for a large number?of different, sometimes difficult,oxidations (e.g. cytochrome P450s, NO synthases, and heme peroxidases).A key question is the nature of the oxy-ferryl heme species (FeIV=O),and?whether or not this is protonated. Previous estimates of bond lengthsfrom?EXAFS/crystallography data vary, and the picture is made more complicatedby photoreduction?effects in synchrotron experiments. ??We present crystalstructures of an authentic Compound I from cytochrome c peroxidase andan authentic Compound II from the closely related ascorbate peroxidase,allowing direct comparison of the bond lengths. We have also used neutrondiffraction to visualise active site protons and their role in Compound Iformation. Comparisons will be made to the corresponding species in other hemeenzymes.

Nature of the ferryl heme species in Compounds I and II

240th National Meeting (2010)

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