RESONANCE RAMAN STUDIES OF OXYCYTOCHROME P450CAM - EFFECT OF SUBSTRATE STRUCTURE ON NU(O-O) AND NU(FE-O2)

Resonance Raman spectra of dioxygen adducts of cytochrome P450cam, in the presence of various substrates, and their biomimetic analogues are reported. The oxidation marker band, nu-4, of oxycytochrome P450cam is observed at 1374 cm-1, which is lower than that of oxyhemeproteins possessing histidyl as a proximal ligand, reflecting the presence of a strong electron-releasing thiolate axial ligand. Both the nu(O-O) and nu(Fe-O2) modes are simultaneously observed and identified (by using O-16(2)/O-18(2) isotopic Substitution technique) at 1140 cm-1 and 541 cm-1, respectively for camphor-bound oxygenated cytochrome P450cam. When camphor is replaced with adamantanone, two lines at 1139 cm-1 and 1147 cm-1 are observed for the nu(O-O) mode, while no significant change in heme core structure is discerned. The substantially lowered frequencies of the nu(O-O) and nu(Fe-O2) and their sensitivity to the variation of the substrate structure provide a structural basis for cleavage of thc bound dioxygen to generate a region and stereospecific hydroxylation agent.