Reorganization energies of the electron transfer reactions involving quinones in the reaction center of Rhodobacter sphaeroides

Abstract

In framework of the continuum electrostatics theory, the reorganization energies of the electron transfers Q-Q (fast phase), Bph-Q, P-Q, and P-Q in the photosynthetic bacterial reaction center have been calculated. The calculations were based on the static dielectric permittivity spatial distribution derived from the data on the electrogenesis, with the corresponding characteristic times relatively close to the reaction times of Q-Q (fast phase) and Bph-Q but much shorter than those times of the latter two recombination reactions. The calculated reorganization energies were reasonably close to the experimental estimates for Q-Q (fast phase) and Bph-Q but substantially lower than those of P-Q and P-Q. A higher effective dielectric permittivity contributes to this effect, but the dominant contribution is most probably made by a non-dielectric relaxation, especially for the P-Q recombination influenced by the proton transfer. This situation calls for reconsidering of the current electron transfer rate estimates.

Correlating structural assemblies of photosynthetic reaction centers on a gold electrode and the photocurrent - potential response

“…For low coverage RC monolayers prepared using 0.5 to 2.5 μM RC, the reorganization energies were on average 0.24 0.03 eV and = +257 19 mV/SHE. The reorganization energies are similar to values reported in the literature for surface-bound RCs ( Trammell et al., 2007 ), but smaller than for the to Q B electron transfer in RCs in solution ( Ptushenko and Krishtalik, 2018 ). Interestingly, one of the surfaces prepared with 5 μM RC showed similar results, but a repeat of this preparation had a larger reorganization energy (0.29 eV) and a more negative of +217 mV/SHE (shown in Supplemental information , Figure S10 ).…”

Active-Site Environmental Factors Customize the Photophysics of Photoenzymatic Old Yellow Enzymes

“…While hydrogen-bonding networks have been invoked in explaining anomalous photoinduced ET behavior within proteins, they have not yet been described within a part of the active-site dielectric environment except theoretically. , Thus, when some of those tyrosine residues are absent, like in MR, OYE1, or the relevant OPR1 mutants, the hydrogen-bonding network might break down and reduce the reorganization energy associated with ET, or those replacement amino acids may not have large changes in orientation upon ET. This is likely related to literature discussions of “nondielectric reorganization energy,” similar to how one might think about internal reorganization energy for ET processes, but for the molecules in the surrounding environment instead of the ET donor and acceptor. ,, These nondielectric contributions to the reorganization energy are thought to come from changes in the position or orientation of nearby charged residues or water molecules within the active site, but changes in hydrogen-bonding networks have so far not been implicated for nondielectric reorganization energy contributions to biological ET events. Clearly, a more detailed experimental investigation into the contributions of the solvent medium and explicit protein medium is necessary for a complete understanding of the role that these distant tyrosine residues have in the reorganization energy for ET in protein active sites.…”

“…This is likely related to literature discussions of "nondielectric reorganization energy," similar to how one might think about internal reorganization energy for ET processes, but for the molecules in the surrounding environment instead of the ET donor and acceptor. 42,44,77 These nondielectric contributions to the reorganization energy are thought to come from changes in the position or orientation of nearby charged residues or water molecules within the active site, but changes in hydrogenbonding networks have so far not been implicated for nondielectric reorganization energy contributions to biological ET events. Clearly, a more detailed experimental investigation into the contributions of the solvent medium and explicit protein medium is necessary for a complete understanding of the role that these distant tyrosine residues have in the reorganization energy for ET in protein active sites.…”

The Photoprotective Protein PsbS from Green Microalga Lobosphaera incisa: The Amino Acid Sequence, 3D Structure and Probable pH-Sensitive Residues

“…In these calculations, we used the approach developed in our previous works [53,54] and based it on accounting for dielectric heterogeneity of the protein. To assess the spatial distribution of dielectric permittivity (ε) within a protein, we employed correlation between local concentration of polar groups in a definite protein volume, on the one hand, and the static dielectric permittivity of the same volume, on the other hand.…”