title: Electron paramagnetic resonance spectroscopy of lactoperoxidase complexes: clarification of hyperfine splitting for the NO adduct of lactoperoxidase.
abstract: Electron paramagnetic resonance (EPR) studies of the nitrosyl adduct of ferrous lactoperoxidase (LPO) confirm that the fifth axial ligand in LPO is bound to the iron via a nitrogen atom. Complete reduction of the ferric LPO sample is required in order to observe the nine-line hyperfine splitting in the ferrous LPO/NO EPR spectrum. The ferrous LPO/NO complex does not exhibit a pH or buffer system dependence when examined by EPR. Interconversion of the ferrous LPO/NO complex and the ferric LPO/NO2- complex is achieved by addition of the appropriate oxidizing or reducing agent. Characterization of the low-spin LPO/NO2- complex by EPR and visible spectroscopy is reported. The pH dependence of the EPR spectra of ferric LPO and ferric LPO/CN- suggests that a high-spin anisotropic LPO complex is formed at high pH and an acid-alkaline transition of the protein conformation near the heme site does occur in LPO/CN-. The effect of tris(hydroxymethyl)aminomethane buffer on the LPO EPR spectrum is also examined.
authors.affiliation: Department of Chemistry, University of Iowa, Iowa City 52242.
authors.forename: G S
authors.initials: GS
authors.lastname: Lukat
authors.forename: K R
authors.initials: KR
authors.lastname: Rodgers
authors.forename: H M
authors.initials: HM
authors.lastname: Goff
mesh_terms: D000818:Animals; D002417:Cattle; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007784:Lactoperoxidase / Q000378:metabolism*; D008892:Milk / Q000201:enzymology; D009569:Nitric Oxide / Q000378:metabolism*; D010544:Peroxidases / Q000378:metabolism*; D011485:Protein Binding
chemical_list: D009569:Nitric Oxide; D007784:Lactoperoxidase; D010544:Peroxidases