title: Electron-transfer chemistry of Ru-linker-(heme)-modified myoglobin: rapid intraprotein reduction of a photogenerated porphyrin cation radical.
abstract: We report the synthesis and characterization of RuC7, a complex in which a heme is covalently attached to a [Ru(bpy)(3)](2+) complex through a -(CH(2))(7)- linker. Insertion of RuC7 into horse heart apomyoglobin gives RuC7Mb, a Ru(heme)-protein conjugate in which [Ru(bpy)(3)](2+) emission is highly quenched. The rate of photoinduced electron transfer (ET) from the resting (Ru(2+)/Fe(3+)) to the transient (Ru(3+)/Fe(2+)) state of RuC7Mb is >10(8) s(-1); the back ET rate (to regenerate Ru(2+)/Fe(3+)) is 1.4 x 10(7) s(-1). Irreversible oxidative quenching by [Co(NH(3))(5)Cl](2+) generates Ru(3+)/Fe(3+): the Ru(3+) complex then oxidizes the porphyrin to a cation radical (P*+); in a subsequent step, P*+ oxidizes both Fe(3+) (to give Fe(IV)=O) and an amino acid residue. The rate of intramolecular reduction of P*+ is 9.8 x 10(3) s(-1); the rate of ferryl formation is 2.9 x 10(3) s(-1). Strong EPR signals attributable to tyrosine and tryptophan radicals were recorded after RuC7MbM(3+) (M = Fe, Mn) was flash-quenched/frozen.
authors.affiliation: Department of Chemistry, University of California, Irvine, California 92697-2025, USA.
authors.forename: Chad E
authors.initials: CE
authors.lastname: Immoos
authors.forename: Angel J
authors.initials: AJ
authors.lastname: Di Bilio
authors.forename: Michael S
authors.initials: MS
authors.lastname: Cohen
authors.forename: Wytze
authors.initials: W
authors.lastname: Van der Veer
authors.forename: Harry B
authors.initials: HB
authors.lastname: Gray
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Farmer
mesh_terms: D000818:Animals; D001059:Apoproteins / Q000737:chemistry*; D002412:Cations / Q000737:chemistry; D004579:Electron Transport; D005609:Free Radicals; D006418:Heme / Q000737:chemistry*; D006736:Horses; D015394:Molecular Structure; D009211:Myoglobin / Q000737:chemistry*; D010084:Oxidation-Reduction; D011166:Porphyrins / Q000737:chemistry*; D017433:Protein Structure, Secondary; D012428:Ruthenium / Q000737:chemistry*
chemical_list: D001059:Apoproteins; D002412:Cations; D005609:Free Radicals; D009211:Myoglobin; D011166:Porphyrins; C010857:apomyoglobin; D006418:Heme; D012428:Ruthenium