Protein Dynamics Control of Electron Transfer in Photosynthetic Reaction Centers from Rps. Sulfoviridis

Abstract

In the cycle of photosynthetic reaction centers, the initially oxidized special pair of bacteriochlorophyll molecules is subsequently reduced by an electron transferred over a chain of four hemes of the complex. Here, we examine the kinetics of electron transfer between the proximal heme c-559 of the chain and the oxidized special pair in the reaction center from Rps. sulfoviridis in the range of temperatures from 294 to 40 K. The experimental data were obtained for three redox states of the reaction center, in which one, two, or three nearest hemes of the chain are reduced prior to special pair oxidation. The experimental kinetic data are analyzed in terms of a Sumi-Marcus-type model developed in our previous paper,1 in which similar measurements were reported on the reaction centers from Rps. viridis. The model allows us to establish a connection between the observed nonexponential electron-transfer kinetics and the local structural relaxation dynamics of the reaction center protein on the microsecond time scale. The activation energy for relaxation dynamics of the protein medium has been found to be around 0.1 eV for all three redox states, which is in contrast to a value around 0.4-0.6 eV in Rps. viridis.1 The possible nature of the difference between the reaction centers from Rps. viridis and Rps. sulfoviridis, which are believed to be very similar, is discussed. The role of the protein glass transition at low temperatures and that of internal water molecules in the process are analyzed.

Energetics and Kinetics of Primary Charge Separation in Bacterial Photosynthesis

“…This assumption certainly breaks down for our problem combining the extremely short time of natural primary charge separation (ca. 3 ps) with the disperse relaxation spectrum of the protein/water solvent. ,,, What we face here is the obvious case of ergodicity breaking of the nuclear fluctuations involved in the reaction activation, which raises the question of how to approach the calculation of the reaction rates.…”

“…3 ps) with the disperse relaxation spectrum of the protein/water solvent. 13,30,66,67 What we face here is the obvious case of ergodicity breaking 68 of the nuclear fluctuations involved in the reaction activation, which raises the question of how to approach the calculation of the reaction rates.…”

Theory of Coupled Electron and Proton Transfer Reactions

“…This distribution should be considered as changing in a self-consistent manner together with the progress of the reaction, as in the Sumi-Marcus type models of electron transfer, see e.g. Refs 103,104…”

Recent Advances in the Theory and Molecular Simulation of Biological Electron Transfer Reactions

“…Moreover, quantum dynamical schemes were developed that aim at solving the time-dependent Schrödinger equation in a product basis of electronic and nuclear wave functions . To account for (ii) and (iii), Woodbury and co-workers, and subsequently Chaudhury et al, modeled the experimental population decay with the diffusion-reaction equation, which was originally developed by Sumi and Marcus (see also ref ). To address (iv), Marchi and co-workers extended the spin-boson model to handle three diabatic states that are coupled to a harmonic bath (=protein environment), respectively. , I shall discuss more recent theoretical developments for the treatment of ultrafast ET reactions in section .…”