Horse muscle myoglobin (Mb) was tightly immobilized at Au-deposited similar to 15-angstrom-thick mixed-type (1:1) alkanethiol SAMs, HS-(CH2)(11)-COOH/HS-(CH2)1, 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 degrees 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 degrees 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 cm(3) mol(-1); and pH-dependent solvent kinetic isotope effect ((KHKD0)-K-0/), 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-(CH2)(11)-COOH junction. In vivo, Mb apparently forms a natural electrostatic complex with cytochrome b(s) (cyt-b(s)) 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.