pH sensitivity of the redox state of cytochrome b559 may regulate its function as a protectant against donor and acceptor side photoinhibition

1995 ◽  
Vol 46 (1-2) ◽  
pp. 193-202 ◽  
Author(s):  
Jayier De Las Rivas ◽  
Judith Klein ◽  
James Barber
Keyword(s):  
Redox State ◽  
Ph Sensitivity ◽  
Cytochrome B559 ◽  
Acceptor Side ◽  
Donor And Acceptor

Molecular Basis of the Vulnerability of Photosystem II to Damage by Light

1995 ◽  
Vol 22 (2) ◽  
pp. 201 ◽  
Author(s):  
J Barber
Keyword(s):  
Triplet State ◽  
Singlet Oxygen ◽  
D1 Protein ◽  
Primary Electron ◽  
In Vivo Studies ◽  
Cytochrome B559 ◽  
Acceptor Side ◽  
Donor And Acceptor ◽  
Primary Cleavage

Using isolated reaction centres and cores of photosystem I1 (PSII) it has been possible to elucidate the details of two separate pathways which lead to photoinhibition. The acceptor side pathway involves charge recombination resulting in the formation of the triplet state of the primary electron donor, P680. This triplet state is harmless in the absence of oxygen but in its presence gives rise to highly reactive singlet oxygen. We have shown that this singlet oxygen specifically attacks the chlorophyll of P680 itself. This process, plus other possibilities, gives rise to degradation of Dl protein involving a primary cleavage in the stromal loop joining putative transmembrane regions four and five, to yield 23 kDa N-terminal and 10 kDa C-terminal fragments. In contrast a donor side pathway is oxygen independent and is due to detrimental secondary oxidations brought about by P680+. Oxidation of accessory chlorophyll (C670) and β-carotene are observed and D1 protein is degraded by a primary cleavage in the lumenal loop between the putative transmembrane segments one and two to yield 24 kDa C-terminal and 9 kDa N-terminal fragments. In vivo studies indicate that the acceptor pathway is more common. The reason for the inherent vulnerability of PSII to photoinduced damage is discussed in terms of the special nature of P68O and the implications of the role of cytochrome b559 as a versatile protectant against donor and acceptor side photoinactivation is also considered. The likely dimeric organisation of PSII in vivo adds an additional factor to the general discussion of the molecular processes which underlie the vulnerability of PSII to photoinduced damage.

scholarly journals A functional model for the role of cytochrome b559 in the protection against donor and acceptor side photoinhibition

1993 ◽  
Vol 90 (23) ◽  
pp. 10942-10946 ◽  
Author(s):  
J Barber ◽  
J De Las Rivas
Keyword(s):  
Reaction Center ◽  
Functional Model ◽  
Anaerobic Conditions ◽  
Cytochrome B559 ◽  
Irreversible Damage ◽  
Strong Light ◽  
Acceptor Side ◽  
Donor And Acceptor ◽  
Potential Form

A quinone-independent photoreduction of the low potential form of cytochrome b559 has been studied using isolated reaction centers of photosystem II. Under anaerobic conditions, the cytochrome can be fully reduced by exposure to strong illumination without the addition of any redox mediators. Under high light conditions, the extent and rate of the reduction is unaffected by addition of the exogenous electron donor Mn2+ and, during this process, no irreversible damage occurs to the reaction center. However, prolonged illumination in strong light brings about irreversible bleaching of chlorophyll, indicative of photoinhibitory damage. When the cytochrome is fully reduced and excess Mn2+ is present, the effect of moderate light is to facilitate the photoaccumulation of reduced pheophytin. The dark reoxidation of the reduced cytochrome is very slow under anaerobic conditions but significantly speeded up on addition of oxidized 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone. From these results it is suggested that the low potential form of cytochrome b559 can accept electrons directly from reduced pheophytin and in so doing help to protect the reaction center against acceptor side photoinhibition as suggested by Nedbal et al. [Nedbal, J., Samson, G. & Whitmarsh, J. (1992) Proc. Natl. Acad. Sci. USA 89, 7929-7933]. This conclusion has been incorporated into a model that further suggests that in its high potential form the cytochrome primarily acts to protect against donor side photoinhibition due to increased lifetime of highly oxidized species as previously proposed by Thompson and Brudvig [Thompson, L. & Brudvig, G. W. (1988) Biochemistry 27, 6653-6658]. The particular feature of our scheme is that it incorporates reversible interconversion between the two redox forms so as to protect against either type of photoinhibition.

Dynamic measurements of mitochondrial hydrogen peroxide concentration and glutathione redox state in rat pancreatic β-cells using ratiometric fluorescent proteins: confounding effects of pH with HyPer but not roGFP1

2012 ◽  
Vol 441 (3) ◽  
pp. 971-978 ◽  
Author(s):  
Leticia P. Roma ◽  
Jessica Duprez ◽  
Hilton K. Takahashi ◽  
Patrick Gilon ◽  
Andreas Wiederkehr ◽  
...  
Keyword(s):  
Hydrogen Peroxide ◽  
Redox State ◽  
Fluorescent Dyes ◽  
Fluorescent Protein ◽  
Fluorescent Proteins ◽  
Ph Sensitivity ◽  
Fluorescence Ratio ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Glutathione Redox

Using the ROS (reactive oxygen species)-sensitive fluorescent dyes dichlorodihydrofluorescein and dihydroethidine, previous studies yielded opposite results about the glucose regulation of oxidative stress in insulin-secreting pancreatic β-cells. In the present paper, we used the ratiometric fluorescent proteins HyPer and roGFP1 (redox-sensitive green fluorescent protein 1) targeted to mitochondria [mt-HyPer (mitochondrial HyPer)/mt-roGFP1 (mitochondrial roGFP1)] to monitor glucose-induced changes in mitochondrial hydrogen peroxide concentration and glutathione redox state in adenovirus-infected rat islet cell clusters. Because of the reported pH sensitivity of HyPer, the results were compared with those obtained with the mitochondrial pH sensors mt-AlpHi and mt-SypHer. The fluorescence ratio of the mitochondrial probes slowly decreased (mt-HyPer) or increased (mt-roGFP1) in the presence of 10 mmol/l glucose. Besides its expected sensitivity to H2O2, mt-HyPer was also highly pH sensitive. In agreement, changes in mitochondrial metabolism similarly affected mt-HyPer, mt-AlpHi and mt-SypHer fluorescence signals. In contrast, the mt-roGFP1 fluorescence ratio was only slightly affected by pH and reversibly increased when glucose was lowered from 10 to 2 mmol/l. This increase was abrogated by the catalytic antioxidant Mn(III) tetrakis (4-benzoic acid) porphyrin but not by N-acetyl-L-cysteine. In conclusion, due to its pH sensitivity, mt-HyPer is not a reliable indicator of mitochondrial H2O2 in β-cells. In contrast, the mt-roGFP1 fluorescence ratio monitors changes in β-cell mitochondrial glutathione redox state with little interference from pH changes. Our results also show that glucose acutely decreases rather than increases mitochondrial thiol oxidation in rat β-cells.

scholarly journals Overexpression of 2-Cys Prx increased salt tolerance of photosystem Ⅱ(PSⅡ) in tobacco

2016 ◽  
Author(s):  
Hui-hui Zhang ◽  
Nan Xu ◽  
Xin Li ◽  
Si-yu Gu
Keyword(s):  
Salt Stress ◽  
Salt Tolerance ◽  
Complex Function ◽  
Photochemical Efficiency ◽  
Active Oxygen ◽  
Gene Overexpression ◽  
Sod Activity ◽  
Tobacco Leaves ◽  
Acceptor Side ◽  
Donor And Acceptor

To explore the plant active oxygen scavenging and photosynthesis function of 2-Cys Prx, a newly discovered member of the antioxidant protease family, the tobacco 2-Cys Prx gene was cloned into the plant expression vector prok Ⅱ. This vector, which is controlled by the constitutive strong promoter CaMV35S, was introduced into tobacco by Agrobacteria-mediated transformation. The 816-bp open reading frame of tobacco 2-Cys Prx encodes 271 amino acids and showed high homology with 2-Cys Prx genes from Solanum lycopersicum, Vitis vinifera, and Populus trichocarpa, indicating 2-Cys Prx gene is highly conserved. The active oxygen metabolism and chlorophyll fluorescence response to salt stress were also studied. Under salt stress, superoxide dismutase (SOD) activity in tobacco leaves increased, while ascorbate peroxidase (APX) activity decreased. Additionally, the donor- and acceptor-side function of photosystem Ⅱ (PSⅡ) were affected by salt stress to different degrees, with the latter significantly more affected than the former. The H2O2 and malondialdehyde content of 2-Cys Prx-overexpression tobacco leaves under salt stress were all significantly lower than those of wild-type (CK) leaves. The PSⅡ maximum photochemical efficiency (Fv/Fm) and the performance index on absorption basis (PIABS) of 2-Cys Prx-overexpression leaves were significantly lower than those of CK leaves under salt stress. Various relative fluorescence intensities of the 2-Cys Prx-overexpression plants exhibited significantly lower increases in amplitude than those of CK plants. Thus, 2-Cys Prx increased the salt tolerance of PSⅡ function and lowered the PSⅡ light inhibition effect in plants under salt stress, suggesting that 2-Cys Prx gene overexpression can alleviate H2O2 buildup and lower the peroxide levels of cytomembrane lipids under salt stress. Thus, 2-Cys Prx gene overexpression can protect oxygen-evolving complex function at the donor side of PSⅡ under salt stress and also improve electron transfer at the acceptor side of PSⅡ.

Interaction of Halogenated 1,4-Benzoquinones with System II of Photosynthesis

1987 ◽  
Vol 42 (6) ◽  
pp. 698-703 ◽  
Author(s):  
Gernot Renger ◽  
Angela Kayed ◽  
Walter Oettmeier
Keyword(s):  
Enzyme System ◽  
Covalent Binding ◽  
Fluorescence Induction ◽  
Ps Ii ◽  
Allosteric Interaction ◽  
Acceptor Side ◽  
Induction Curve ◽  
Donor And Acceptor ◽  
The Stability ◽  
Oxygen Yield

The interaction of halogenated p-benzoquinones with PS II has been analyzed by measurements of fluorescence induction curves and the average oxygen yield per flash in isolated class II chloroplasts. It was found: 1)The normalized area over the fluorescence induction curve in the presence of DCMU. A/Fmax, markedly increases if halogenated p-benzoquinones are added before DCMU. The effect is eliminated by DCMU addition prior to that of the quinones. 2)The extent of A/Fmax increases with increasing dark time between the additions of 2,3.5-tri- bromo-6-methyl-1,4-benzoquinone (TBTO) and DCMU. respectively. 3) Some of the halogenated p-benzoquinones were found to act as efficient electron acceptors under repetitive excitation at low flash frequency (2 Hz). In the case of TBTO and 2,3-di-chloro-5-t-butyl-1,4-benzoquinone (TBU 13) the sensitivity of the average oxygen yield per flash was shifted towards higher concentrations of DCMU. 4) Halogenated p-benzoquinones can also affect the stability of oxidizing redox equivalents in the water oxidizing enzyme system Y. This effect depends on the nature of the substituents. The present results are interpreted by the assumption of a covalent binding of halogenated p-benzoquinones in the vicinity of Qᴀ. This binding is prevented by DCMU. The possibility of allosteric interaction between the donor and acceptor side of PS II is discussed.

scholarly journals Alteration of photosystem II properties with non-photochemical excitation quenching

2000 ◽  
Vol 355 (1402) ◽  
pp. 1405-1418 ◽  
Author(s):  
A. Laisk ◽  
V. Oja
Keyword(s):  
Photosystem Ii ◽  
Turnover Rate ◽  
Photochemical Quenching ◽  
Ps Ii ◽  
Single Turnover ◽  
Acceptor Side ◽  
Donor And Acceptor ◽  
Inhibitory Type ◽  
Non Photochemical Quenching ◽  
Oxygen Yield

Oxygen yield from single turnover flashes and multiple turnover pulses was measured in sunflower leaves differently pre–illuminated to induce either ‘energy–dependent type’ non–photochemical excitation quenching ( q E ) or reversible, inhibitory type non–photochemical quenching ( q I ). A zirconium O 2 analyser, combined with a flexible gas system, was used for these measurements. Oxygen yield from saturating single turnover flashes was the equivalent of 1.3–2.0 μmol e − m −2 in leaves pre–adapted to low light. It did not decrease when q E quenching was induced by a 1 min exposure to saturating light, but it decreased when pre–illumination was extended to 30–60 min. Oxygen evolution from saturating multiple turnover pulses behaved similarly: it did not decrease with the rapidly induced q E but decreased considerably when exposure to saturating light was extended or O 2 concentration was decreased to 0.4%. Parallel recording of chlorophyll fluorescence and O 2 evolution during multiple turnover pulses, interpreted with the help of a mathematical model of photosystem II (PS II) electron transport, revealed PS II donor and acceptor side resistances. These experiments showed that PS II properties depend on the type of non–photochemical quenching present. The rapidly induced and rapidly reversible q E type (photoprotective) quenching does not induce changes in the number of active PS II or in the PS II maximum turnover rate, thus confirming the antenna mechanism of q E. The more slowly induced but still reversible q I type quenching (photoinactivation) induced a decrease in the number of active PS II and in the maximum PS II turnover rate. Modelling showed that, mainly, the acceptor side resistance of PS II increased in parallel with the reversible q I. Oxygen yield from single turnover flashes and multiple turnover pulses was measured in sunflower leaves differently pre–illuminated to induce either ‘energy–dependent type’ non–photochemical excitation quenching ( q E ) or reversible, inhibitory type non–photochemical quenching ( q I ). A zirconium O 2 analyser, combined with a flexible gas system, was used for these measurements. Oxygen yield from saturating single turnover flashes was the equivalent of 1.3–2.0 μmol e − m −2 in leaves pre–adapted to low light. It did not decrease when q E quenching was induced by a 1 min exposure to saturating light, but it decreased when pre–illumination was extended to 30–60 min. Oxygen evolution from saturating multiple turnover pulses behaved similarly: it did not decrease with the rapidly induced q E but decreased considerably when exposure to saturating light was extended or O 2 concentration was decreased to 0.4%. Parallel recording of chlorophyll fluorescence and O 2 evolution during multiple turnover pulses, interpreted with the help of a mathematical model of photosystem II (PS II) electron transport, revealed PS II donor and acceptor side resistances. These experiments showed that PS II properties depend on the type of non–photochemical quenching present. The rapidly induced and rapidly reversible q E type (photoprotective) quenching does not induce changes in the number of active PS II or in the PS II maximum turnover rate, thus confirming the antenna mechanism of q E. The more slowly induced but still reversible q I type quenching (photoinactivation) induced a decrease in the number of active PS II and in the maximum PS II turnover rate. Modelling showed that, mainly, the acceptor side resistance of PS II increased in parallel with the reversible q I.

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