title: Quantum chemical interpretation of the spectral properties of the CO and O2 complexes of hemoglobin and cytochrome P-450.
abstract: The electronic transitions of CO and O2 complexes of hemoglobin and cytochrome P-450 were calculated using a PPP method extended for metal complexes. The calculations show that the unusual spectral properties of cytochrome P-450 are very sensitive to the iron-sulfur bond distance. It is suggested from these calculations that for the conversion of cytochrome P-450 to cytochrome P-420 an increase of the iron-sulfur bond distance of only about 0.2 A is sufficient. The anomalous Soret band of the CO complex as well as the normal Soret band of the O2 complex of cytochrome P-450 are explicable assuming a mercaptide sulfur as fifth ligand.
mesh_terms: D000818:Animals; D001665:Binding Sites; D002248:Carbon Monoxide; D002263:Carboxyhemoglobin; D002417:Cattle; D003577:Cytochrome P-450 Enzyme System; D006454:Hemoglobins; D007501:Iron; D008024:Ligands; D008297:Male; D010100:Oxygen; D010108:Oxyhemoglobins; D011485:Protein Binding; D011789:Quantum Theory; D011817:Rabbits; D013053:Spectrophotometry
chemical_list: D006454:Hemoglobins; D008024:Ligands; D010108:Oxyhemoglobins; D002248:Carbon Monoxide; D003577:Cytochrome P-450 Enzyme System; D002263:Carboxyhemoglobin; D007501:Iron; D010100:Oxygen