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Start Over Descriptor "ELECTRON-TRANSFER KINETICS" Topic photosynthesis
3 results on '"ELECTRON-TRANSFER KINETICS"'

1. Alternative Fast and Slow Primary Charge-Separation Pathways in Photosystem II.

Author

Capone M, Sirohiwal A, Aschi M, Pantazis DA, and Daidone I

Subjects
Chlorophyll metabolism, Oxidation-Reduction, Photosystem II Protein Complex metabolism, Photosynthesis
Abstract

Photosystem-II (PSII) is a multi-subunit protein complex that harvests sunlight to perform oxygenic photosynthesis. Initial light-activated charge separation takes place at a reaction centre consisting of four chlorophylls and two pheophytins. Understanding the processes following light excitation remains elusive due to spectral congestion, the ultrafast nature, and multi-component behaviour of the charge-separation process. Here, using advanced computational multiscale approaches which take into account the large-scale configurational flexibility of the system, we identify two possible primary pathways to radical-pair formation that differ by three orders of magnitude in their kinetics. The fast (short-range) pathway is dominant, but the existence of an alternative slow (long-range) charge-separation pathway hints at the evolution of redundancy that may serve other purposes, adaptive or protective, related to formation of the unique oxidative species that drives water oxidation in PSII., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Published
2023
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2. Alternative Fast and Slow Primary Charge‐Separation Pathways in Photosystem II.

Author

Capone, Matteo, Sirohiwal, Abhishek, Aschi, Massimiliano, Pantazis, Dimitrios A., and Daidone, Isabella

Subjects
OXIDATION of water, HARVESTING, PHOTOSYSTEMS, PHOTOSYNTHESIS, CHLOROPHYLL
Abstract

Photosystem‐II (PSII) is a multi‐subunit protein complex that harvests sunlight to perform oxygenic photosynthesis. Initial light‐activated charge separation takes place at a reaction centre consisting of four chlorophylls and two pheophytins. Understanding the processes following light excitation remains elusive due to spectral congestion, the ultrafast nature, and multi‐component behaviour of the charge‐separation process. Here, using advanced computational multiscale approaches which take into account the large‐scale configurational flexibility of the system, we identify two possible primary pathways to radical‐pair formation that differ by three orders of magnitude in their kinetics. The fast (short‐range) pathway is dominant, but the existence of an alternative slow (long‐range) charge‐separation pathway hints at the evolution of redundancy that may serve other purposes, adaptive or protective, related to formation of the unique oxidative species that drives water oxidation in PSII. [ABSTRACT FROM AUTHOR]

Published
2023
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3. Trehalose matrix effects on charge-recombination kinetics in Photosystem I of oxygenic photosynthesis at different dehydration levels

Author

Marco Malferrari, Mahir D. Mamedov, Giovanni Venturoli, Georgy E. Milanovsky, Anton Savitsky, Alexey Yu. Semenov, Klaus Möbius, Wolfgang Lubitz, Malferrari, Marco, Savitsky, Anton, Mamedov, Mahir D., Milanovsky, Georgy E., Lubitz, Wolfgang, Möbius, Klau, Semenov, Alexey Yu., and Venturoli, Giovanni

Subjects
0301 basic medicine, SP PCC 6803, Kinetics, Biophysics, ELECTRON-TRANSFER KINETICS, 010402 general chemistry, Photosystem I, Photochemistry, 01 natural sciences, Biochemistry, law.invention, 03 medical and health sciences, chemistry.chemical_compound, Electron transfer, law, HIGH-FIELD EPR, Photosynthesis, Electron paramagnetic resonance, P700, Photosystem I Protein Complex, Protein dynamics, CONFORMATIONAL DYNAMICS, Electron Spin Resonance Spectroscopy, Trehalose, Humidity, Cell Biology, PROTEIN DYNAMICS, MOLECULAR-DYNAMICS SIMULATION, 0104 chemical sciences, DIFFERENT HYDRATION LEVELS, Oxygen, Crystallography, ROOM-TEMPERATURE, 030104 developmental biology, Solvation shell, chemistry, BACTERIAL REACTION CENTERS, EXTERNAL MATRIX
Abstract

Matrix effects on long-range electron transfer were studied in cyanobacterial Photosystem I (PS I) complexes, embedded into trehalose glasses at different hydration levels. W-band EPR studies demonstrated, via nitroxide spin probes, structural homogeneity of the dry PS I-trehalose matrix and no alteration of cofactors' distance and relative orientation under temperature and matrix variation. In dry trehalose glasses at room temperature (RT), PS I was stable for months. Flash-induced charge recombination kinetics were examined by high-field time-resolved EPR and optical spectroscopies. The kinetics in hydrated PS I-trehalose glasses mostly reflected the reduction of the photooxidized primary donor P700•+ by the reduced terminal iron-sulfur clusters. Upon dehydration, the P700•+ decay accelerated and became more distributed. Continuous distributions of lifetimes τ were extracted from the kinetics by two numerical approaches: a maximum entropy method (MemExp program) and a constrained regularization method (CONTIN program). Both analyses revealed that upon dehydration the contribution of the two slowest components (lifetimes τ ~ 300 ms and ~ 60 ms), attributed to P700•+[FA/FB] − recombination, decreased in parallel with the increase of the fastest component (τ ~ 150 μs), and of additional distributed phases with intermediate lifetimes. Dehydration at RT mimicked the effects of freezing water-glycerol PS I systems, suggesting an impairment of PS I protein dynamics in the dry trehalose glass. Similar effects were observed previously in bacterial reaction centers. The work presented for PS I provides new insights into the crucial issue of protein-matrix interactions for protein functionality as controlled by hydrogen-bond networks of the hydration shell.

Published
2015

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