title: Strength of axial water ligation in substrate-free cytochrome P450s is isoform dependent.
abstract: The heme-containing cytochrome P450s exhibit isoform-dependent ferric spin equilibria in the resting state and differential substrate-dependent spin equilibria. The basis for these differences is not well understood. Here, magnetic circular dichroism (MCD) reveals significant differences in the resting low spin ligand field of CYPs 3A4, 2E1, 2C9, 125A1, and 51B1, which indicates differences in the strength of axial water ligation to the heme. The near-infrared bands that specifically correspond to charge-transfer porphyrin-to-metal transitions span a range of energies of nearly 2 kcal/mol. In addition, the experimentally determined MCD bands are not entirely in agreement with the expected MCD energies calculated from electron paramagnetic resonance parameters, thus emphasizing the need for the experimental data. MCD marker bands of the high spin heme between 500 and 680 nm were also measured and suggest only a narrow range of energies for this ensemble of high spin Cys(S(-)) → Fe(3+) transitions among these isoforms. The differences in axial ligand energies between CYP isoforms of the low spin states likely contribute to the energetics of substrate-dependent spin state perturbation. However, these ligand field energies do not correlate with the fraction of high spin vs low spin in the resting state enzyme, suggestive of differences in water access to the heme or isoform-dependent differences in the substrate-free high spin states as well.
authors.affiliation: Departments of Medicinal Chemistry Box 357610 and ‡Chemistry Box 351700, University of Washington Seattle , Washington 98195 United States.
authors.forename: Kip P
authors.initials: KP
authors.lastname: Conner
authors.forename: Alina M
authors.initials: AM
authors.lastname: Schimpf
authors.forename: Alex A
authors.initials: AA
authors.lastname: Cruce
authors.forename: Kirsty J
authors.initials: KJ
authors.lastname: McLean
authors.forename: Andrew W
authors.initials: AW
authors.lastname: Munro
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Frank
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Krzyaniak
authors.forename: Paul
authors.initials: P
authors.lastname: Ortiz de Montellano
authors.forename: Michael K
authors.initials: MK
authors.lastname: Bowman
authors.forename: William M
authors.initials: WM
authors.lastname: Atkins
mesh_terms: D002942:Circular Dichroism; D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D008026:Ligation; D020033:Protein Isoforms / Q000737:chemistry; D014867:Water / Q000737:chemistry*
chemical_list: D020033:Protein Isoforms; D014867:Water; D003577:Cytochrome P-450 Enzyme System