title: Model systems for the coordination chemistry of cytochrome P-450.
abstract: Studies on model complexes have supported the presence of a mercaptide as the fifth ligand of cytochrome P-450 monooxygenases. When alcohol or thiol ligands are added to the sixth coordination position of a five-coordinated 4-nitrobenzene thiolate complex of FeIII protoporphyrin IX dimethyl ester chloride low spin complexes with optical and EPR-spectra very similar to cytochrome P-450 are obtained. From a comparison with all ligands of cytochrome P-450 and the model complexes it is concluded that a hard ligands must occupy the sixth coordination position of cytochrome P-450. An imidazole group is less likely, also in view of the ligand field parameters. The significance of the fifth and sixth ligand of cytochrome P-450 is discussed with respect to the monooxygenase mechanism.
mesh_terms: D003577:Cytochrome P-450 Enzyme System; D004578:Electron Spin Resonance Spectroscopy; D007501:Iron; D008024:Ligands; D006899:Mixed Function Oxygenases; D008954:Models, Biological; D011166:Porphyrins; D011485:Protein Binding; D011524:Protoporphyrins; D013113:Spin Labels
chemical_list: D008024:Ligands; D011166:Porphyrins; D011524:Protoporphyrins; D013113:Spin Labels; D003577:Cytochrome P-450 Enzyme System; D007501:Iron; D006899:Mixed Function Oxygenases