Structural analysis of compound I in hemoproteins: study on Proteus mirabilis catalase

Ferryl catalysis has attracted considerable interest, because a diverse variety of enzymes use ferryl intermediates to perform difficult chemistry. The structure of the reactional intermediate compound I of Proteus mirabilis catalase (PMC) has been solved using time-resolved X-ray diffraction techniques and single crystal microspectrophotometry. Formation of compound I is characterized by significant changes in the absorbance spectrum, and the creation of an oxoferryl group on the distal side of the heme. This group is clearly visible in the X-ray electron density maps. An unidentified electron density, likely to be an anion because of the nature of its environment, appears during the reaction, in a site distant from the heme. The structure of compound I in PMC is compared with that of compound I in cytochrome c peroxidase (CCP).