title: Cytochrome P-450 spin state: inorganic biochemistry of haem iron ligation and functional significance.
abstract: Haem ligation in cytochrome P-450 has been reviewed and the nature of the fifth and sixth ligands of the haemoprotein in the ferric low-spin, ferric high-spin, ferrous and ferrous-carbon-monoxy states have been discussed. Factors controlling the cytochrome P-450 spin equilibrium have been described, including substrate and functional components of the mixed-function oxidase system. In addition, a thermodynamic model describing the interaction of substrate with ferric cytochrome P-450 has been developed in terms of the micro-equilibrium constants governing substrate binding. The functional significance of the cytochrome P-450 spin state with particular reference to control of the first electron reduction of the haemoprotein has been summarized, and a subsequent validation of the spin-redox coupling model of cytochrome P-450-dependent catalysis has been presented.
mesh_terms: D000818:Animals; D002248:Carbon Monoxide / Q000378:metabolism; D002384:Catalysis; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D005290:Ferric Compounds / Q000378:metabolism; D005296:Ferrous Compounds / Q000378:metabolism; D006418:Heme / Q000378:metabolism*; D006801:Humans; D007501:Iron / Q000378:metabolism*; D007700:Kinetics; D008024:Ligands; D009249:NADP / Q000378:metabolism; D010101:Oxygen Consumption; D011487:Protein Conformation
chemical_list: D005290:Ferric Compounds; D005296:Ferrous Compounds; D008024:Ligands; D006418:Heme; D009249:NADP; D002248:Carbon Monoxide; D003577:Cytochrome P-450 Enzyme System; D007501:Iron