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Electron Transfer Route between Quinones in Type-II Reaction Centers.

ABSTRACT: In photosynthetic reaction centers from purple bacteria (PbRCs) and photosystem II (PSII), the photoinduced charge separation is terminated by an electron transfer between the primary (Q_A) and secondary (Q_B) quinones. Here, we investigate the electron transfer route, calculating the superexchange coupling (H_QA-QB) for electron transfer from Q_A to Q_B in the protein environment. H_QA-QB is significantly larger in PbRC than in PSII. In superexchange electron tunneling, the electron transfer via unoccupied molecular orbitals of the nonheme Fe complex (Q_A → Fe → Q_B) is pronounced in PbRC, whereas the electron transfer via occupied molecular orbitals (Fe → Q_B followed by Q_A → Fe) is pronounced in PSII. The significantly large H_QA-QB is caused by a water molecule that donates the H-bond to the ligand Glu-M234 in PbRC. The corresponding water molecule is absent in PSII due to the existence of D1-Tyr246. H_QA-QB increases in response to the Ser-L223···Q_B H-bond formation caused by an extension of the H-bond network, which facilitates charge delocalization over the Q_B site. This explains the observed discrepancy in the Q_A-to-Q_B electron transfer between PbRC and PSII, despite their structural similarity.

SUBMITTER: Sugo Y

PROVIDER: S-EPMC9707520 | biostudies-literature | 2022 Nov

REPOSITORIES: biostudies-literature

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Electron Transfer Route between Quinones in Type-II Reaction Centers.

Sugo Yu Y Tamura Hiroyuki H Ishikita Hiroshi H

The journal of physical chemistry. B 20221114 46

In photosynthetic reaction centers from purple bacteria (PbRCs) and photosystem II (PSII), the photoinduced charge separation is terminated by an electron transfer between the primary (QA) and secondary (QB) quinones. Here, we investigate the electron transfer route, calculating the superexchange coupling (HQA-QB) for electron transfer from QA to QB in the protein environment. HQA-QB is significantly larger in PbRC t ...[more]

PMID: 36374126

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Project description:Long-distance electron transfer in marine environments couples physically separated redox half-reactions, impacting biogeochemical cycles of iron, sulfur and carbon. Bacterial bio-electrochemical systems that facilitate electron transfer via conductive filaments or across man-made electrodes are well-known, but the impact of abiotic currents across naturally occurring conductive and semiconductive minerals is poorly understood. In this paper I use cyclic voltammetry to explore electron transfer between electrodes made of common iron minerals (magnetite, hematite, pyrite, pyrrhotite, mackinawite, and greigite), and hydroquinones-a class of organic molecules found in carbon-rich sediments. Of all tested minerals, only pyrite and magnetite showed an increase in electric current in the presence of organic molecules, with pyrite showing excellent electrocatalytic performance. Pyrite electrodes performed better than commercially available glassy carbon electrodes and showed higher peak currents, lower overpotential values and a smaller separation between oxidation and reduction peaks for each tested quinone. Hydroquinone oxidation on pyrite surfaces was reversible, diffusion controlled, and stable over a large number of potential cycles. Given the ubiquity of both pyrite and quinones, abiotic electron transfer between minerals and organic molecules is likely widespread in Nature and may contribute to several different phenomena, including anaerobic respiration of a wide variety of microorganisms in temporally anoxic zones or in the proximity of hydrothermal vent chimneys, as well as quinone cycling and the propagation of anoxic zones in organic rich waters. Finally, interactions between pyrite and quinones make use of electrochemical gradients that have been suggested as an important source of energy for the origins of life on Earth. Ubiquinones and iron sulfide clusters are common redox cofactors found in electron transport chains across all domains of life and interactions between quinones and pyrite might have been an early analog of these ubiquitous systems.

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Electron Transfer Route between Quinones in Type-II Reaction Centers.

Publications

Electron Transfer Route between Quinones in Type-II Reaction Centers.

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