Formation of low spin complexes of ferric cytochrome P-450-CAM with anionic ligands. Spin state and ligand affinity comparison to myoglobin.

In order to further elucidate the electronic structure and ligand coordination properties of cytochrome P-450, we have performed a search for anions which can bind to the heme of P-450-CAM purified from Pseudomonas putida The complexes have been characterized by W-visible absorption and electron paramagnetic resonance spectroscopy.W e have found that (a) a relatively wide variety of anions (L-) that are well known ligands to ferric myoglobin, including CN-, N3-, RS-, RCOO-, SCN-, SeCN-, and OCN-, reversibly bind to ferric P-450 to form bis-anionic complexes [(Cys-S-)Fe"'heme(L-)].Binding of the latter three anions to P-450 has not been previously reported.Retention of the endogenous cysteinate axial ligand of P-450 upon complex formation is confirmed by their narrowspread EPR g values.Except for cyanide, these ligands are competitively replaced by the substrate, camphor.