Light-induced reduction of bovine adrenodoxin via the covalently bound ruthenium(II) bipyridyl complex: intramolecular electron transfer and crystal structure.
Bovine adrenodoxin (Adx) plays an important role in the electron-transfer process in the mitochondrial steroid hydroxylase system of the bovine adrenal cortex. Using electron paramagnetic resonance (EPR) spectroscopy, we showed that photoreduction of the [2Fe-2S] cluster of Adx via (4'-methyl-2,2'-bipyridine)bis(2,2'-bipyridine)ruthenium(II) [Ru(bpy)2(mbpy)] covalently attached to the protein surface can be used as a new approach to probe the "shuttle" hypothesis for the electron transfer by Adx. The 1.5 A resolution crystal structure of a 1:1 Ru(bpy)2(mbpy)-Adx(1-108) complex reveals the site of modification, Cys95, and allows to predict the possible intramolecular electron-transfer pathways within the complex. Photoreduction of uncoupled Adx, mutant Adx(1-108), and Ru(bpy)2(mbpy)-Adx(1-108) using safranin T as the mediating electron donor suggests that two electrons are transferred from the dye to Adx. The intramolecular photoreduction rate constant for the ruthenated Adx has been determined and is discussed according to the predicted pathways.
Halavaty
Andrei
A
Crystallography Group, Max-Delbrück-Centrum für Molekulare Medizin, Robert-Rössle-Strasse 10, D-13125 Berlin-Buch, Germany.
Müller
Jürgen J
JJ
Contzen
Jörg
J
Jung
Christiane
C
Hannemann
Frank
F
Bernhardt
Rita
R
Galander
Marcus
M
Lendzian
Friedhelm
F
Heinemann
Udo
U
D015082:2,2'-Dipyridyl / Q000737:chemistry*; D000325:Adrenodoxin / Q000737:chemistry* / Q000528:radiation effects*; D000818:Animals; D001667:Binding, Competitive; D002417:Cattle; D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy; D004583:Electrons; D007700:Kinetics; D008027:Light; D008958:Models, Molecular; D010084:Oxidation-Reduction / Q000528:radiation effects; D011487:Protein Conformation; D012428:Ruthenium / Q000737:chemistry*
D000325:Adrenodoxin; D015082:2,2'-Dipyridyl; D012428:Ruthenium