The Catalytic Pathway of Cytochrome P450cam at Atomic Resolution

Members of the cytochrome P450 superfamily catalyze the addition of mo-lecular oxygen to nonactivated hydrocarbons at physiological temperatureÑa reaction that requires high temperature to proceed in the absence of a catalyst. Structures were obtained for three intermediates in the hydroxylation reaction of camphor by P450cam with trapping techniques and cryocrystallography. The structure of the ferrous dioxygen adduct of P450cam was determined with 0.91 angstrom wavelength x-rays; irradiation with 1.5 angstrom x-rays results in breakdown of the dioxygen molecule to an intermediate that would be con-sistent with an oxyferryl species. The structures show conformational changes in several important residues and reveal a network of bound water molecules that may provide the protons needed for the reaction. Cytochrome P450 enzymes are ubiquitous heme-containing monooxygenases named for the absorption band at 450 nm of their carbon monoxide (CO) form (1). They are involve