Electronic absorption spectra of native ferric CPO (red), reduced CPO (black), ferric P450CAM (blue), and reduced P450CAM (green). The CPO spectra were recorded at pH 5 in 0.1 M phosphate buffer, and the maximum of the Soret peak is 399 nm for the ferric species and 409 nm for the reduced species. The camphor-bound P450CAM spectra were measured at pH 7 in 0.1 M phosphate buffer, and the maximum of the Soret peak is 392 nm for the ferric species and 414 nm for the reduced species. The spectra have been normalized using published extinction coefficients.