title: Identification of the EPR-active iron-nitrosyl complexes in mammalian ferritins.
abstract: This study was undertaken to characterize the nitric oxide complexes of mammalian ferritin and their EPR properties to gain a better understanding of the interaction of NO with non-heme iron proteins within the cell. Measurements were made with horse spleen apo- and holoferritins, with chemically modified proteins, and with recombinant human H-chain apoferritin and its site-directed mutants. Three types of EPR signals (A, B, and C) have been identified and attributed to iron-nitrosyl complexes at imidazole groups of histidine, thiol groups of cysteine, and carboxylate groups of aspartate and glutamate, respectively. The C-type axial spectrum has features at g perpendicular' = 4 and g parallel' = 2 characteristic of a paramagnetic Fe(3+)-NO- complex with total spin S = 3/2 and probably arises from nonspecific binding to carboxylate groups on the protein. The S = 1/2 axial B-type signal g perpendicular' = 2.033 and g parallel' = 2.014) is formed at Cys-130 (human H-chain sequence numbering). His-128 and possibly His-118 are sites of formation of the rhombic S = 1/2 A-type complex (gx' = 2.055, gy' = 2.033, and gz' = 2.015); the former residue perhaps plays a role in the conformational stability of the protein as well as in iron binding. The data reveal that the residues Cys-130 and His-128 in the vicinity of 3-fold channels leading to the interior of the protein shell are important in iron-nitrosyl complex formation in mammalian ferritins.
authors.affiliation: Department of Chemistry, University of New Hampshire, Durham 03824.
authors.forename: M
authors.initials: M
authors.lastname: Lee
authors.forename: P
authors.initials: P
authors.lastname: Arosio
authors.forename: A
authors.initials: A
authors.lastname: Cozzi
authors.forename: N D
authors.initials: ND
authors.lastname: Chasteen
mesh_terms: D000818:Animals; D001052:Apoferritins / Q000737:chemistry / Q000378:metabolism; D002729:Chloromercuribenzoates / Q000494:pharmacology; D004578:Electron Spin Resonance Spectroscopy; D005293:Ferritins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006736:Horses; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry / Q000378:metabolism*; D008667:Metalloproteins / Q000737:chemistry / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D009569:Nitric Oxide / Q000737:chemistry / Q000378:metabolism*; D019159:Nonheme Iron Proteins; D013329:Structure-Activity Relationship; D020245:p-Chloromercuribenzoic Acid
chemical_list: D002729:Chloromercuribenzoates; D008667:Metalloproteins; D019159:Nonheme Iron Proteins; D009569:Nitric Oxide; D020245:p-Chloromercuribenzoic Acid; D005293:Ferritins; D001052:Apoferritins; D007501:Iron