Photoactivation of Oxygen Evolution of Wheat Photosystem II Membranes Depleted of Manganese Atoms
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Oxygen evolution
Oxygen-evolving complex
In photosynthesis, photosystem II evolves oxygen from water by the accumulation of photooxidizing equivalents at the oxygen-evolving complex (OEC). The OEC is a Mn 4 CaO 5 cluster, and its sequentially oxidized states are termed the S n states. The dark-stable state is S 1 , and oxygen is released during the transition from S 3 to S 0 . In this study, a laser flash induces the S 1 to S 2 transition, which corresponds to the oxidation of Mn(III) to Mn(IV). A broad infrared band, at 2,880 cm −1 , is produced during this transition. Experiments using ammonia and 2 H 2 O assign this band to a cationic cluster of internal water molecules, termed “W 5 + .” Observation of the W 5 + band is dependent on the presence of calcium, and flash dependence is observed. These data provide evidence that manganese oxidation during the S 1 to S 2 transition results in a coupled proton transfer to a substrate-containing, internal water cluster in the OEC hydrogen-bonded network.
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The Mn4Ca complex bound to photosystem II (PSII) is the active site of photosynthetic water oxidation. Its assembly involves binding and light-driven oxidation of manganese, a process denoted as photoactivation. The disassembly of the Mn complex is a thermally activated process involving distinct intermediates. Starting from intermediate states of the disassembly, which was initiated by a temperature jump to 47 °C, we photoactivated PSII membrane particles and monitored the activity recovery by O2 polarography and delayed chlorophyll fluorescence measurements. Oxidation state and structural features of the formed intermediates of the Mn complex were assayed by X-ray absorption spectroscopy at the Mn K-edge. The photoactivation time courses, which exhibit a lag phase characteristic of intermediate formation only when starting with the apo-PSII, suggest that within ∼5 min of photoactivation of apo-PSII, a binuclear Mn complex is formed. It is proposed that a MnIII2(di-μ-oxo) complex is a key intermediate both in the disassembly and in the assembly reaction paths.
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Conference Article| February 01 1986 Polypeptide depletion of Photosystem II and recovery of oxygen evolution by addition of specific ions DAVID J. CHAPMAN; DAVID J. CHAPMAN 1Photosynthesis Research Group, Department of Pure and Applied Biology, Imperial College, London SW7 2BB, U.K. Search for other works by this author on: This Site PubMed Google Scholar JOHN DE FELICE JOHN DE FELICE 1Photosynthesis Research Group, Department of Pure and Applied Biology, Imperial College, London SW7 2BB, U.K. Search for other works by this author on: This Site PubMed Google Scholar Biochem Soc Trans (1986) 14 (1): 38–39. https://doi.org/10.1042/bst0140038 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn MailTo Cite Icon Cite Get Permissions Citation DAVID J. CHAPMAN, JOHN DE FELICE; Polypeptide depletion of Photosystem II and recovery of oxygen evolution by addition of specific ions. Biochem Soc Trans 1 February 1986; 14 (1): 38–39. doi: https://doi.org/10.1042/bst0140038 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsBiochemical Society Transactions Search Advanced Search This content is only available as a PDF. © 1986 Biochemical Society1986 Article PDF first page preview Close Modal You do not currently have access to this content.
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Abstract Water oxidation and concomitant dioxygen formation by the manganese-calcium cluster of oxygenic photosynthesis has shaped the biosphere, atmosphere, and geosphere. It has been hypothesized that at an early stage of evolution, before photosynthetic water oxidation became prominent, light-driven formation of manganese oxides from dissolved Mn(2+) ions may have played a key role in bioenergetics and possibly facilitated early geological manganese deposits. Here we report the biochemical evidence for the ability of photosystems to form extended manganese oxide particles. The photochemical redox processes in spinach photosystem-II particles devoid of the manganese-calcium cluster are tracked by visible-light and X-ray spectroscopy. Oxidation of dissolved manganese ions results in high-valent Mn(III,IV)-oxide nanoparticles of the birnessite type bound to photosystem II, with 50-100 manganese ions per photosystem. Having shown that even today’s photosystem II can form birnessite-type oxide particles efficiently, we propose an evolutionary scenario, which involves manganese-oxide production by ancestral photosystems, later followed by down-sizing of protein-bound manganese-oxide nanoparticles to finally yield today’s catalyst of photosynthetic water oxidation.
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Photosynthetic water oxidation, where water is oxidized to dioxygen, is a fundamental chemical reaction that sustains the biosphere. This reaction is catalyzed by a Mn4Ca complex in the photosystem II (PS II) oxygen-evolving complex (OEC): a multiprotein assembly embedded in the thylakoid membranes of green plants, cyanobacteria, and algae. The mechanism of photosynthetic water oxidation by the Mn4Ca cluster in photosystem II is the subject of much debate, although lacking structural characterization of the catalytic intermediates. Biosynthetically exchanged Ca/Sr-PS II preparations and x-ray spectroscopy, including extended x-ray absorption fine structure (EXAFS), allowed us to monitor Mn-Mn and Ca(Sr)-Mn distances in the four intermediate S states, S0 through S3, of the catalytic cycle that couples the one-electron photochemistry occurring at the PS II reaction center with the four-electron water-oxidation chemistry taking place at the Mn4Ca(Sr) cluster. We have detected significant changes in the structure of the complex, especially in the Mn-Mn and Ca(Sr)-Mn distances, on the S2-to-S3 and S3-to-S0 transitions. These results implicate the involvement of at least one common bridging oxygen atom between the Mn-Mn and Mn-Ca(Sr) atoms in the O-O bond formation. Because PS II cannot advance beyond the S2 state in preparations that lack Ca(Sr), these results show that Ca(Sr) is one of the critical components in the mechanism of the enzyme. The results also show that Ca is not just a spectator atom involved in providing a structural framework, but is actively involved in the mechanism of water oxidation and represents a rare example of a catalytically active Ca cofactor.
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The reconstitution of water-oxidizing complex (WOC) with a Mn2Ca mixed metal complex in manganese-depleted photosystem II was for the first time reported. The Mn2Ca complex was shown to be more effective in restoring electron transfer and oxygen evolution capacity during photoactivation in comparison with that of MnCl2. It was proposed that the carboxylato bridge between the Ca and Mn atoms may benefit the formation and stability of the Mn cluster.
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