Tiwari, Arjun*
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The effect of illumination and molecular oxygen on the redox and the redox potential changes of cytochrome b(559) (cyt b(559)) has been studied in Tris-treated spinach photosystem II (PSII) membranes. It has been demonstrated that the illumination of Tris-treated PSII membranes induced the conversion of the intermediate-potential (IP) to the reduced high-potential (HP(Fe2+)) form of cyt b(559), whereas the removal of molecular oxygen resulted in the conversion of the IP form to the oxidized high-potential (HP(Fe3+)) form of cyt b(559). Light-induced conversion of cyt b(559) from the IP to the HP form was completely inhibited above pH 8 or by the modification of histidine ligand that prevents its protonation. Interestingly, no effect of high pH or histidine modification was observed during the conversion of the IP to the HP form of cyt b(559) after the removal of molecular oxygen. These results indicate that conversion from the IP to the HP form of cyt b(559) proceeds via different mechanisms. Under illumination, conversion of the IP to the HP form of cyt b(559) depends primarily on the protonation of the histidine residue, whereas under anaerobic conditions, the conversion of the IP to the HP form of cyt b(559) is driven by higher hydrophobicity of the environment around the heme iron resulting from the absence of molecular oxygen.
- MeSH
- chemické modely MeSH
- cytochromy typu b chemie metabolismus MeSH
- fotosystém II (proteinový komplex) chemie metabolismus MeSH
- histidin chemie metabolismus MeSH
- koncentrace vodíkových iontů MeSH
- kyslík metabolismus farmakologie MeSH
- oxidace-redukce účinky léků účinky záření MeSH
- potenciometrie MeSH
- rostlinné proteiny chemie metabolismus MeSH
- spektrofotometrie MeSH
- Spinacia oleracea metabolismus MeSH
- světlo MeSH
- tromethamin chemie farmakologie MeSH
- tylakoidy účinky léků metabolismus účinky záření MeSH
- železité sloučeniny chemie metabolismus MeSH
- železnaté sloučeniny chemie metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
In this study, electron paramagnetic resonance spin-trapping spectroscopy was used to study the light-induced production of superoxide anion (O2 (•-)) and carbon-centered (R(•)) radicals by Photosystem II (PSII). It is evidenced here that exposure of PSII membranes to high light (2,000 μmol photons m(-2) s(-1)) or heat (47 °C) treatments prior to the illumination suppressed O2 (•-) production, while R(•) was formed. Formation of R(•) in the both high light- and heat-treated PSII membranes was enhanced by DCMU. Removal of molecular oxygen by glucose/glucose oxidase/catalase system and O2 (•-) scavenging by exogenous superoxide dismutase completely suppressed carbon-centered radical formation. It is proposed here that the oxidation of polyunsaturated fatty acids and amino acids by O2 (•-) on the electron acceptor side of PSII results in the formation of R(•), known to initiate a cascade reaction leading to the lipid peroxidation and protein degradation, respectively.
- MeSH
- elektronová paramagnetická rezonance MeSH
- fotochemické procesy MeSH
- fotosystém II (proteinový komplex) chemie metabolismus MeSH
- kyslík chemie metabolismus MeSH
- oxidace-redukce MeSH
- spin trapping metody MeSH
- Spinacia oleracea MeSH
- superoxidy chemie metabolismus MeSH
- světlo MeSH
- volné radikály chemie metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
The effect of water-splitting Mn complex on light-induced redox changes of cytochrome b(559) (cyt b(559)) was studied in spinach photosystem II (PSII) membranes. Photoreduction of the heme iron in the intact PSII membranes was completely suppressed by DCMU, whereas photoreduction and photooxidation of the heme iron in the Mn-depleted PSII membranes were unaffected by DCMU. Interestingly, photoreduction and photooxidation of the heme iron in the Mn-depleted PSII membranes were completely diminished by exogenous superoxide dismutase (SOD), whereas no effect of SOD on photoreduction of the heme iron was observed in the intact PSII membranes. The current work shows that the light-induced redox changes of cyt b(559) proceed via a different mechanism in the both types of PSII membranes. In the intact PSII membranes, photoreduction of the heme iron is mediated by plastoquinol. However, in the Mn-depleted PSII membranes, photoreduction and photooxidation of the heme iron are mediated by superoxide anion radical formed in PSII.
- MeSH
- cytochromy typu b chemie metabolismus MeSH
- fotosystém II (proteinový komplex) chemie metabolismus MeSH
- konformace proteinů MeSH
- mangan nedostatek metabolismus MeSH
- oxidace-redukce MeSH
- rostlinné proteiny metabolismus MeSH
- Spinacia oleracea metabolismus MeSH
- voda metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
The Arabidopsis mutant rcd1 is tolerant to methyl viologen (MV). MV enhances the Mehler reaction, i.e. electron transfer from Photosystem I (PSI) to O2, generating reactive oxygen species (ROS) in the chloroplast. To study the MV tolerance of rcd1, we first addressed chloroplast thiol redox enzymes potentially implicated in ROS scavenging. NADPH-thioredoxin oxidoreductase type C (NTRC) was more reduced in rcd1. NTRC contributed to the photosynthetic and metabolic phenotypes of rcd1, but did not determine its MV tolerance. We next tested rcd1 for alterations in the Mehler reaction. In rcd1, but not in the wild type, the PSI-to-MV electron transfer was abolished by hypoxic atmosphere. A characteristic feature of rcd1 is constitutive expression of mitochondrial dysfunction stimulon (MDS) genes that affect mitochondrial respiration. Similarly to rcd1, in other MDS-overexpressing plants hypoxia also inhibited the PSI-to-MV electron transfer. One possible explanation is that the MDS gene products may affect the Mehler reaction by altering the availability of O2. In green tissues, this putative effect is masked by photosynthetic O2 evolution. However, O2 evolution was rapidly suppressed in MV-treated plants. Transcriptomic meta-analysis indicated that MDS gene expression is linked to hypoxic response not only under MV, but also in standard growth conditions. This article is part of the theme issue 'Retrograde signalling from endosymbiotic organelles'.
