Resonance Raman detection of bound dioxygen in cytochrome P-450(cam)

We have used resonance Raman spectroscopy and isotopic labeling techniques to unambiguously assign the dioxygen stretching frequency (v̄(o-o)) in the substrate-bound oxygenated complex of cytochrome P-450(cam). The frequency found for v̄(o-o) in the P-450(cam) system (1140 cm^-1) is in remarkable agreement with recent studies of thiolate heme model compounds. The general features of the oxy-P-450(cam) Raman spectra are tabulated and comparisons are made with the oxy complexes of hemoglobin, myoglobin, and various model compounds. Most of the results are qualitatively explained by consideration of electron donation into the π(g)*(O₂)/dπ(M) orbitals of the oxygenated complex (M = Fe or Co). It is also noted that the effect of the 'extra' electron in the nitrogen base Co(II) oxy complexes, in some ways, parallels the effect of the lone pair electrons of thiolate in the oxy-P-450(cam) complex. This is evidenced by the enhanced resonance Raman activity of v̄(o-o) in both the Co(II) and P-450 systems as well as by the similarity of the v̄(o-o) frequencies.