scholarly journals Electron, proton and hydrogen–atom transfers in photosynthetic water oxidation

2002 ◽  
Vol 357 (1426) ◽  
pp. 1383-1394 ◽  
Author(s):  
Cecilia Tommos
Keyword(s):  
Photosystem Ii ◽  
Proton Transfer ◽  
Water Oxidation ◽  
Oxidation Mechanism ◽  
Bulk Solution ◽  
Hydrogen Atoms ◽  
Redox Active ◽  
Hydrogen Atom Transfers ◽  
Reduce Carbon Dioxide ◽  
Photosynthetic Water Oxidation

When photosynthetic organisms developed so that they could use water as an electron source to reduce carbon dioxide, the stage was set for efficient proliferation. Algae and plants spread globally and provided the foundation for our atmosphere and for O 2 –based chemistry in biological systems. Light–driven water oxidation is catalysed by photosystem II, the active site of which contains a redox–active tyrosine denoted Y Z , a tetramanganese cluster, calcium and chloride. In 1995, Gerald Babcock and co–workers presented the hypothesis that photosynthetic water oxidation occurs as a metallo–radical catalysed process. In this model, the oxidized tyrosine radical is generated by coupled proton/electron transfer and re–reduced by abstracting hydrogen atoms from substrate water or hydroxide–ligated to the manganese cluster. The proposed function of Y Z requires proton transfer from the tyrosine site upon oxidation. The oxidation mechanism of Y Z in an inhibited and O 2 –evolving photosystem II is discussed. Domino–deprotonation from Y Z to the bulk solution is shown to be consistent with a variety of data obtained on metal–depleted samples. Experimental data that suggest that the oxidation of Y Z in O 2 –evolving samples is coupled to proton transfer in a hydrogen–bonding network are described. Finally, a dielectric–dependent model for the proton release that is associated with the catalytic cycle of photosystem II is discussed.

scholarly journals Water oxidation chemistry of photosystem II

2007 ◽  
Vol 363 (1494) ◽  
pp. 1211-1219 ◽  
Author(s):  
Gary W Brudvig
Keyword(s):  
Photosystem Ii ◽  
Water Oxidation ◽  
Oxidation Mechanism ◽  
Intermediate Species ◽  
X Ray ◽  
Redox Active ◽  
Ca Ions ◽  
Oxidation Chemistry ◽  
Chemical Problem ◽  
Mechanism Of The Reaction

Photosystem II (PSII) uses light energy to split water into protons, electrons and O 2 . In this reaction, nature has solved the difficult chemical problem of efficient four-electron oxidation of water to yield O 2 without significant amounts of reactive intermediate species such as superoxide, hydrogen peroxide and hydroxyl radicals. In order to use nature's solution for the design of artificial catalysts that split water, it is important to understand the mechanism of the reaction. The recently published X-ray crystal structures of cyanobacterial PSII complexes provide information on the structure of the Mn and Ca ions, the redox-active tyrosine called Y Z and the surrounding amino acids that comprise the O 2 -evolving complex (OEC). The emerging structure of the OEC provides constraints on the different hypothesized mechanisms for O 2 evolution. The water oxidation mechanism of PSII is discussed in the light of biophysical and computational studies, inorganic chemistry and X-ray crystallographic information.

scholarly journals Untangling the sequence of events during the S2→ S3transition in photosystem II and implications for the water oxidation mechanism

2020 ◽  
Vol 117 (23) ◽  
pp. 12624-12635 ◽  
Author(s):  
Mohamed Ibrahim ◽  
Thomas Fransson ◽  
Ruchira Chatterjee ◽  
Mun Hon Cheah ◽  
Rana Hussein ◽  
...  
Keyword(s):  
Photosystem Ii ◽  
Water Oxidation ◽  
Donor Site ◽  
Oxidation Mechanism ◽  
Oxygenic Photosynthesis ◽  
Acceptor Site ◽  
Oxygen Evolving Complex ◽  
Ps Ii ◽  
Sequence Of Events ◽  
Large Channel

In oxygenic photosynthesis, light-driven oxidation of water to molecular oxygen is carried out by the oxygen-evolving complex (OEC) in photosystem II (PS II). Recently, we reported the room-temperature structures of PS II in the four (semi)stable S-states, S1, S2, S3, and S0, showing that a water molecule is inserted during the S2→ S3transition, as a new bridging O(H)-ligand between Mn1 and Ca. To understand the sequence of events leading to the formation of this last stable intermediate state before O2formation, we recorded diffraction and Mn X-ray emission spectroscopy (XES) data at several time points during the S2→ S3transition. At the electron acceptor site, changes due to the two-electron redox chemistry at the quinones, QAand QB, are observed. At the donor site, tyrosine YZand His190 H-bonded to it move by 50 µs after the second flash, and Glu189 moves away from Ca. This is followed by Mn1 and Mn4 moving apart, and the insertion of OX(H) at the open coordination site of Mn1. This water, possibly a ligand of Ca, could be supplied via a “water wheel”-like arrangement of five waters next to the OEC that is connected by a large channel to the bulk solvent. XES spectra show that Mn oxidation (τ of ∼350 µs) during the S2→ S3transition mirrors the appearance of OXelectron density. This indicates that the oxidation state change and the insertion of water as a bridging atom between Mn1 and Ca are highly correlated.

scholarly journals The exchange of the fast substrate water in the S2 state of photosystem II is limited by diffusion of bulk water through channels – implications for the water oxidation mechanism

2021 ◽  
Author(s):  
Casper de Lichtenberg ◽  
Christopher J. Kim ◽  
Petko Chernev ◽  
Richard J Debus ◽  
Johannes Messinger
Keyword(s):  
Photosystem Ii ◽  
Molecular Oxygen ◽  
Water Oxidation ◽  
Oxidation Mechanism ◽  
Bulk Water ◽  
Oxygen Species ◽  
S2 State ◽  
Oxo Bridge

The molecular oxygen we breathe is produced from water-derived oxygen species bound to the Mn4CaO5 cluster in photosystem II (PSII). Present research points to the central oxo-bridge O5 as the...

scholarly journals Fast enzymatic HCO3- dehydration supports photosynthetic water oxidation in Photosystem II from pea

2021 ◽  
Author(s):  
Alexandr V. Shitov ◽  
Vasily V. Terentyev ◽  
Govindjee Govindjee
Keyword(s):  
Photosystem Ii ◽  
Pisum Sativum ◽  
Water Oxidation ◽  
Photochemical Reactions ◽  
O2 Evolution ◽  
Donor Side ◽  
Psii Photochemistry ◽  
Similar Dependence ◽  
Enzymatic Nature ◽  
Photosynthetic Water Oxidation

Carbonic anhydrase (CA) activity, associated with Photosystem II (PSII) from Pisum sativum, has been shown to enhance water oxidation. But, the nature of the CA activity, its origin and role in photochemistry has been under debate, since the rates of CA reactions, measured earlier, were less than the rates of photochemical reactions. Here, we demonstrate high CA activity in PSII from Pisum sativum, measured by HCO3- dehydration at pH 6.5 (i.e. under optimal condition for PSII photochemistry), with kinetic parameters Km of 2.7 mM; Vmax of 2.74·10-2 mM·sec-1; kcat of 1.16·103 sec-1 and kcat/Km of 4.1·105 M-1 sec-1, showing the enzymatic nature of this activity, which kcat exceeds by ~13 times the rate of PSII, as measured by O2 evolution. The similar dependence of HCO3- dehydration, of the maximal quantum yield of photochemical reactions and of O2 evolution on the ratio of chlorophyll/photochemical reaction center II demonstrate the interconnection of these processes on the electron donor side of PSII. Since the removal of protons is critical for fast water oxidation, and since HCO3- dehydration consumes a proton, we suggest that CA activity, catalyzing very fast removal of protons, supports efficient water oxidation in PSII and, thus, photosynthesis in general.

scholarly journals Design and synthesis of benzimidazole phenol-porphyrin dyads for the study of bioinspired photoinduced proton-coupled electron transfer

2019 ◽  
Vol 23 (11n12) ◽  
pp. 1336-1345
Author(s):  
S. Jimena Mora ◽  
Daniel A. Heredia ◽  
Emmanuel Odella ◽  
Uma Vrudhula ◽  
Devens Gust ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Excited State ◽  
Photosystem Ii ◽  
Proton Transfer ◽  
Water Oxidation ◽  
Oxidation Catalyst ◽  
Design And Synthesis ◽  
Proton Coupled Electron Transfer ◽  
Anchoring Groups ◽  
High Redox Potential

Benzimidazole phenol-porphyrin dyads have been synthesized to study proton-coupled electron transfer (PCET) reactions induced by photoexcitation. High-potential porphyrins have been chosen to model P680, the photoactive chlorophyll cluster of photosynthetic photosystem II (PSII). They have either two or three pentafluorophenyl groups at the meso positions to impart the high redox potential. The benzimidazole phenol (BIP) moiety models the Tyr[Formula: see text]-His190 pair of PSII, which is a redox mediator that shuttles electrons from the water oxidation catalyst to P680[Formula: see text]. The dyads consisting of a porphyrin and an unsubstituted BIP are designed to study one-electron one-proton transfer (E1PT) processes upon excitation of the porphyrin. When the BIP moiety is substituted with proton-accepting groups such as imines, one-electron two-proton transfer (E2PT) processes are expected to take place upon oxidation of the phenol by the excited state of the porphyrin. The bis-pentafluorophenyl porphyrins linked to BIPs provide platforms for introducing a variety of electron-accepting moieties and/or anchoring groups to attach semiconductor nanoparticles to the macrocycle. The triads thus formed will serve to study the PCET process involving the BIPs when the oxidation of the phenol is achieved by the photochemically produced radical cation of the porphyrin.

Sign in / Sign up

Export Citation Format

Share Document