Long-Range Electron Transfer in Ruthenium-Modified Cytochromes c. σ-Tunneling Pathways through Aromatic Residues

摘要: The rates of intramolecular electron-transfer (ET) reactions from the ferroheme to bis(2,2'-bipyridine)(imidazole)-ruthenium(II1) complexes bound genetically engineered histidines (58 and 66) on surface yeast iso-1-cytochrome c (cyt c) have been measured by using a laser flashquench technique. crystal structure of the wild-type protein indicates that ET pathways involve aromatic side chains: Ru(His58)cyt includes a bridging tryptophan at position 59, Ru(His66)cyt has tyrosine 67. A variant in which bridging Tyr67 His66 mutant had replaced with phenylalanine also was examined. Fe^2+ → Ru^(3+)ET rate constants (25 °C, pH 7.0) are as follows: 5.2(5) × l0^4 (ΔE° = 0.69(5)), c; 1.0(1) 10^6 (ΔE° 0.72(5)), 3.1(3) l0^6 s^-1 0.77(5) eV), Ru(His66Phe67)cyt c. experimentally derived electronic coupling [H_AB(His66)= 0.014; H_AB(HiS66)= 0.060 cm-1 closer agreement lengths a-tunneling than direct donor-acceptor distances, there is no indication u orbitals intervening groups enhance any these couplings. Maximum modified cytochromes drop 2 orders magnitude for every 6.3-A increase length. Analysis results suggests an internal water molecule plays role linking Ru(His66) group heme.