title: Angular dependence of electron paramagnetic resonances of an azide-NO complex of cytochrome c oxidase: orientation of the haem-copper axis in cytochrome aa3 from ox heart.
abstract: The orientation dependence of the EPR signals arising from the azide-nitric oxide complex of cytochrome oxidase was investigated using oriented multilayers of mitochondrial membranes from ox heart. Variations in line shape of the DeltaMS=1 signal of the triplet state were apparent, whilst the DeltaMS=2 transitions between g=4.7 and 3.9 varied in intensity as the angle of the applied magnetic field was varied. These half-field signals were maximal with the field parallel to the membrane plane. A model of the bi-liganded azide-nitric oxide complex has been constructed, in which the nitric oxide is bound to the high-spin haem in a bent configuration, with the Fe-N=O plane at 60-90 degrees to the membrane plane and the azide bound to the copper, distal from the haem. In addition, angular variations of the signals at g'=11 and g' around 3.5, derived from an integer-spin complex, were also observed.
authors.affiliation: School of Biological and Medical Sciences, University of St. Andrews, St. Andrews, Fife, Scotland, KY16 9AL, UK.
authors.forename: D J
authors.initials: DJ
authors.lastname: Hunter
authors.forename: J C
authors.initials: JC
authors.lastname: Salerno
authors.forename: W J
authors.initials: WJ
authors.lastname: Ingledew
mesh_terms: D000818:Animals; D001386:Azides; D002417:Cattle; D003300:Copper / Q000032:analysis; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D003576:Electron Transport Complex IV / Q000737:chemistry* / Q000378:metabolism; D006418:Heme / Q000032:analysis; D007501:Iron; D008929:Mitochondria, Heart / Q000201:enzymology*; D009569:Nitric Oxide; D012418:Ruminants
chemical_list: D001386:Azides; D009569:Nitric Oxide; D006418:Heme; D003300:Copper; D007501:Iron; D003576:Electron Transport Complex IV