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Dolidze T.D.,ritashvili Center For Experimental Biomedicine | Dolidze T.D.,Tbilisi State University | Dolidze T.D.,Friedrich - Alexander - University, Erlangen - Nuremberg | Shushanyan M.,ritashvili Center For Experimental Biomedicine | And 4 more authors.
Journal of Coordination Chemistry | Year: 2015

The naturally occurring electron-transfer (ET) event for myoglobin (Mb) can be mimicked through its functionalization at diversely modified metal platforms to allow for the electron exchange either in freely diffusing or immobilized regimes. In this work, horse muscle Mb was involved in the electron exchange with Au electrodes modified by dissimilar, thin or thick alkanethiol SAMs, terminated either by unicomponent (-OH) or 1: 1 mixed (-OH/-COOH) functional (externally exposed) entities, respectively. The systematic, temperature- and pressure-supported cyclic voltammetry studies perfectly confirmed certainty of two kinds of ET patterns for Mb, embodying: (a) different operational kinetic regimes (including proteins freely diffusing and strongly confined motifs) and (b) different intrinsic physical mechanisms (including dynamically controlled and non-adiabatic modes). Our analysis of obtained and published data for Mb and the reference redox-active protein, cytochrome c, specified further the central mechanistic role of the Fe-(heme-)coordinated water whose displacement is directly coupled to ET, and can be, in turn, controlled by the conformational organization and intrinsic fluctuational mobility of the Mb macromolecule. © 2015 Taylor & Francis.

Khoshtariya D.E.,Friedrich - Alexander - University, Erlangen - Nuremberg | Khoshtariya D.E.,Tbilisi State University | Khoshtariya D.E.,ritashvili Center For Experimental Biomedicine | Dolidze T.D.,Friedrich - Alexander - University, Erlangen - Nuremberg | And 6 more authors.
Journal of Physical Chemistry B | Year: 2014

Horse muscle myoglobin (Mb) was tightly immobilized at Au-deposited ∼15-Å-thick mixed-type (1:1) alkanethiol SAMs, HS-(CH 2)11-COOH/HS-(CH2)11-OH, and placed in contact with buffered H2O or D2O solutions. Fast-scan cyclic voltammetry (CV) and a Marcus-equation-based analysis were applied to determine unimolecular standard rate constants and reorganization free energies for electron transfer (ET), under variable-temperature (15-55 C) and -pressure (0.01-150 MPa) conditions. The CV signal was surprisingly stable and reproducible even after multiple temperature and pressure cycles. The data analysis revealed the following values: standard rate constant, 33 s -1 (25 C, 0.01 MPa, H2O); reorganization free energy, 0.5 ± 0.1 eV (throughout); activation enthalpy, 12 ± 3 kJ mol -1; activation volume, -3.1 ± 0.2 cm3 mol -1; and pH-dependent solvent kinetic isotope effect (kH0 /kD0), 0.7-1.4. Furthermore, the values for the rate constant and reorganization free energy are very similar to those previously found for cytochrome c electrostatically immobilized at the monocomponent Au/HS-(CH 2)11-COOH junction. In vivo, Mb apparently forms a natural electrostatic complex with cytochrome b5 (cyt-b5) through the "dynamic" (loose) docking pattern, allowing for a slow ET that is intrinsically coupled to the water's removal from the "defective" heme iron (altogether shaping the biological repair mechanism for Mb's "met" form). In contrary, our experiments rather mimic the case of a "simple" (tight) docking of the redesigned (mutant) Mb with cyt-b 5 (Nocek et al. J. Am. Chem. Soc. 2010, 132, 6165-6175). According to our analysis, in this configuration, Mb's distal pocket (linked to the "ligand channel") seems to be arrested within the restricted configuration, allowing the rate-determining reversible ET process to be coupled only to the inner-sphere reorganization (minimal elongation/shortening of an Fe-OH2 bond) rather than the pronounced detachment (rebinding) of water and, hence, to be much faster. © 2013 American Chemical Society.

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