Electron-Transfer Chemistry of Ru−Linker−(Heme)-Modified Myoglobin:  Rapid Intraprotein Reduction of a Photogenerated Porphyrin Cation Radical

Abstract

Top trace is the residual from the fit of back electron transfer (Ru 3+ Fe 2+ → Ru 2+ Fe 3+ ; k = 1.7 x 10 7 sec -1 ). The Ru 3+ Fe 2+ state is formed at >10 8 s -1 . In the transient difference spectra (not shown), the absorbance increase due to formation of RuC7MbFe 2+ and the corresponding bleach due to loss of RuC7MbFe 3+ both occur within 10 ns.

Electrochemical generation of a high-valent state of cytochrome P450

“…3) shows that E is inhibited, in accord with a redox reaction involving a water-ligated Fe III heme. Replacing the axial water with another ligand (imidazole in this case) would inhibit ferryl formation, as previously reported [25]. This finding also rules against the alternative interpretation that E is a tyrosine or tryptophan redox couple.…”

Ru(II)-diimine functionalized metalloproteins: From electron transfer studies to light-driven biocatalysis

“…Alternatively, several groups have investigated the attachment of Ru(II) photosensitizers directly to protein cofactors (entries 9 and 10) such as the prosthetic heme group [37, 38] in reconstituted heme proteins or the pterin cofactor of the inducible nitric oxide synthase. [39]…”

“…The strong MLCT band can be detected in covalent adducts of metalloproteins even in the presence of the strong absorbing Soret band of the heme cofactor. [38, 40, 41] Measurements of the excited state lifetime can also provide valuable information regarding the local environment around the photosensitizer. [28, 42] Using mass spectrometry, a characteristic shift in the mass of the protein is observed upon covalent attachment of the photosensitizer.…”

“…In the case of myoglobin where the original cofactor could be replaced by a Ru(II)-modified heme, a porphyrin radical has been observed in two separate studies followed by formation of Compound II (Fe(IV)=O) in one case [37] or an amino acid radical in the other. [38] For the covalently modified pterin cofactor, rapid heme reduction of the inducible nitric oxide synthase protein was observed[39] but more work is still needed to form valuable reactive intermediates.…”

Contribution of the heme propionate groups to the electron transfer and electrostatic properties of myoglobin

“…Mb is readily autoxidized to metMb in an aerobic environment (reviewed in [9]), and enzymatic reduction of myoglobin to the reduced, Fe(II) state was reported over twenty years ago [10] though the subsequent literature has produced inconsistent results regarding the nature of this enzymatic system (reviewed in [11]). The literature concerning the oxidation-reduction properties and electron transfer kinetics of myoglobin is extensive (a review of the older literature is provided in [12]) and in more recent years has emphasized the use of myoglobin as (i) a model for studies of intramolecular electron transfer (e.g., [13,14]), (ii) a participant in protein-protein electron transfer reactions (e.g., [15][16][17][18]), a model for ligand binding (e.g., [19][20][21][22][23]) and (iv) a protein scaffold for genetic engineering of new functionalities (e.g., [19,[24][25][26][27][28]). …”