Modification of the structural and redox properties of cytochrome c by heteropolytungstate binding.
Complex formation between horse heart ferricytochrome c and large three-dimensional polyanions has been investigated, in order to study the influence of surface electrostatic interactions on the structural and redox properties of cytochrome c. Cytochrome c binds the large heteropolytungstates (NaSb9W21O86)18- and (KAs4W40O140)27- with a 1/1 polyanion/cytochrome c ratio, and the smaller ion (SiW11O39)8- with a 2/1 ratio. Upon complexation, cytochrome c undergoes structural changes that are dependent on the size and charge of the polyanion, and on the pH and ionic strength of the medium. Three different forms of complexed cytochrome c have been characterized by optical and EPR spectroscopies, in the pH range 6.5-8: an N form, close to the native structure, an A form, analogous to cytochrome c in acidic medium, and a novel B form in which the heme pocket is open but the iron remains low-spin. The redox potential of cytochrome c is lowered to 250-220 mV (vs. NHE) in the N form, and to 80 mV in the B form.
Chottard
G
G
Laboratoire de Physicochimie Inorganique, Université Pierre et Marie Curie, France.
Michelon
M
M
Hervé
M
M
Hervé
G
G
D000818:Animals; D000965:Antimony / Q000378:metabolism*; D001151:Arsenic / Q000378:metabolism; D003574:Cytochrome c Group / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D006736:Horses; D006863:Hydrogen-Ion Concentration; D010084:Oxidation-Reduction; D011199:Potentiometry; D012825:Silicon / Q000378:metabolism; D014414:Tungsten / Q000378:metabolism*; D017973:Tungsten Compounds
D003574:Cytochrome c Group; D017973:Tungsten Compounds; C009613:ammonium tungsten antimonate hydroxide oxide; D000965:Antimony; D001151:Arsenic; D014414:Tungsten; D012825:Silicon