Redox metalloproteins

Jensen TJ, Gray HB, Winkler JR, Kuznetsov AM, Ulstrup J. Dynamic ionic strength effects in fast bimolecular electron transfer between a redox metalloprotein of high electrostatic charge and an inorganic reaction partner. J Phys Chem B 2000 104 11556-62. 

Electrochemically controlled SAMs of the alkanethiol class characterized to high voltammetric resolution and to molecular and sub-molecular structural in situ STM resolution have been reviewed recently [60, 151]. We note here first some issues of importance to functionalized alkanethiols as linker molecules for gentle immobilization of fully functional redox metalloprotein monolayers on singlecrystal Au(lll) electrode surfaces. We discuss next specifically the functionalized alkanethiols cysteine (Cys) and homocysteine (Hey). These two molecules represent a core protein building block and a core metabolite, respectively. The former has been used to display unique sub-molecular in situ STM resolution [152]. The latter shows a unique dual surface dynamics pattern that could be followed both by single-molecule in situ STM and by high-resolution capacitive voltammetry. 

Interfadal Electrochemistry and In Situ Imaging of Redox Metalloproteins and Metalloenzymes at the Single-Molecule Level... 

Small Redox Metalloproteins Blue Copper, Heme, and Iron-Sulfur Proteins... 

Cytochrome C4 A Prototype for Microscopic Electronic Mapping of Multicenter Redox Metalloproteins... 

AuNPs inserted between the electrode surface and redox metalloproteins therefore both work as effective molecular linkers and exert eflfident electrocatalysis. Recent considerations based on resonance turmeling between the electrode and the molecule via the AuNP as a mechanism for enhanced interfadal ET rates suggest that electronic spillover rather than energetic resonance is a hkely origin of the effects (J. Kleis et al., work in progress). Even slightly enhanced spillover compared with a planar Au(lll) surface is enough to enhance the ET rate by the observed amount over a 10-15 A ET distance. 

Electronic conductivity of molecules including redox metalloproteins with accessible low-lying redox states in nanogap electrode configurations or in situ STM displays quite different patterns. These are dominated by sequential two-step (or multiple-step) hopping through the redox center, induced both by potential variation and environmental configurahonal fluctuations. Both redox molecules and... 

Facci, P., Alliata, D., and Cannistraro, S. (2001) Potential-induced resonant tunneling through a redox metalloprotein investigated by electrochemical scanning probe microscopy. Ultramicroscopy, 89,... 

Chi, Q.J., Zhang, J.D., Jensen, P.S., Nazmudtinov, R.R., and Ulstrup, J. (2008) Surface-induced intramolecular electron transfer in multi-centre redox metalloproteins the di-haem protein cytochrome q in homogeneous solution and at electrochemical surfaces. Journal of Physics Condensed Matter, 20, 374124. 

One line in bioelectrochemistry is rooted in electrochemical techniques, spectroscopy, and other physical chemical techniques. Linear and cyclic voltammetry are central.Other electrochemical techniques include impedance and electroreflectance spectroscopy," ultramicro-electrodes, and chronoamperometry. To this come spectroscopic techniques such as infiared, surface enhanced Raman and resonance Raman,second harmonic generation, surface Plasmon, and X-ray photoelectron spectroscopy. A second line has been to combine state-of-the-art physical electrochemistry with corresponding state-of-the-art microbiology and chemical S5mthesis. The former relates to the use of a wide range of designed mutant proteins, " the latter to chemical synthesis or de novo designed synthetic redox metalloproteins. " " ... 

With a few exceptions, redox metalloprotein voltammetry on gold surfaces is unstable or absent unless either the electrode is modified by chemisorbed monolayers of linker or promoter molecules, or the protein is modified by insertion of non-native amino acid residues. The linker molecules are usually thiol-containing molecules which adsorb strongly on the Au-surface. 

Overall the single-crystal voltammetry, surface promoter sensitivity, and in situ STM of PJ d illuminate procedures and approaches to highly increased resolution in the bioelectrochemical mapping of redox metalloproteins, approaching the electrochemical resolution of small molecular adsorbate molecules. 

Single-molecule resolution has been achieved for redox metalloproteins, larger redox metalloenz5mies, and DNA-based molecules in surface-confined monolayers on metallic electrode surfaces, where the biological function in natural aqueous environment can be controlled by the electroehemical potential. Not only structural mapping of immobilized redox metalloproteins and DNA-based molecules can be achieved. Given adequate theoretical support, ET and redox enzyme function can also be addressed at this level of resolution. The Os-complexes and the redox... 

---