Crystallographic and Single-Crystal Spectral Analysis of the Peroxidase Ferryl Intermediate

The ferryl [Fe(IV)O] intermediate is important in many heme enzymes, and thus, the precise nature of the Fe(IV)-O bond is critical in understanding enzymatic mechanisms. The 1.40 angstrom crystal structure of cytochrome c peroxidase Compound I has been determined as a function of X-ray dose while the visible spectrum was being monitored. The Fe-O bond increases in length from 1.73 angstrom in the low-X-ray dose structure to 1.90 angstrom in the high-dose structure. The low-dose structure correlates well with an Fe(IV)=O bond, while we postulate that the high-dose structure is the cryo-trapped Fe(III) OH species previously thought to be an Fe(IV) OH species.