Measurement of time-resolved oxygen concentration changes in photosynthetic systems by nitroxide-based EPR oximetry

Strzałka, Kazimierz; Walczak, Tadeusz; Sarna, Tadeusz; Swartz, Harold M.

doi:10.1016/0003-9861(90)90449-9

Cited by 38 publications

(29 citation statements)

References 23 publications

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“…As a consequence, the isotope effect is ascribed to the breakage of hydrogen bonds during electron abstraction from $3 leading to 02 formation. Since the yox reduction by S 3 exhibits almost the same kinetics as oxygen release [36][37][38][39] it is reasonable to assume that this (these) hydrogen bond(s) comprise substrate water. This idea is highly supported by previous findings of an H/D isotope effect on the oxygen release kinetics [40] that is of nearly the same extent as that of the electron transfer from S 3 to yox ( [7], this study).…”

Section: Discussionmentioning

confidence: 99%

Effects of hydrogen/deuterium exchange on photosynthetic water cleavage in PS II core complexes from spinach

et al. 1996

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Section: Discussionmentioning

confidence: 99%

Effects of hydrogen/deuterium exchange on photosynthetic water cleavage in PS II core complexes from spinach

et al. 1996

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“…Nitroxides have a reducible nitroxide group ( · N-O) as part of a five-or six-carbon ring (Soule et al, 2007;Wilcox and Pearlman, 2008). Piperidine nitroxides are a diverse group of stable free radicals classically used as spin probes in electron paramagnetic resonance spectroscopy (Matsumoto et al, 2004), as paramagnetic contrast agents in nuclear magnetic resonance imaging (Bennett et al, 1987), and as oxygen-sensitive probes in biological systems (Strzalka et al, 1990). TEMPO (2,2,6,C 9 H 18 NO,MW 156.25), one of the most commonly used members of the nitroxide family, is a stable nitroxyl radical that has a variety of uses related to its role as radical scavenger and stabilizer.…”

Section: Introductionmentioning

confidence: 99%

Nitroxide TEMPO: A genotoxic and oxidative stress inducer in cultured cells

Guo

Mittelstaedt

Guo

et al. 2013

Toxicology in Vitro

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Abstract2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO) is a low molecular weight nitroxide and stable free radical. In this study, we investigated the cytotoxicity and genotoxicity of TEMPO in mammalian cells using the mouse lymphoma assay (MLA) and in vitro micronucleus assay. In the absence of metabolic activation (S9), 3 mM TEMPO produced significant cytotoxicity and marginal mutagenicity in the MLA; in the presence of S9, treatment of mouse lymphoma cells with 1-2 mM TEMPO resulted in dose-dependent decreases of the relative total growth and increases in mutant frequency. Treatment of TK6 human lymphoblastoid cells with 0.9-2.3 mM TEMPO increased the frequency of both micronuclei (a marker for clastogenicity) and hypodiploid nuclei (a marker of aneugenicity) in a dose-dependent manner; greater responses were produced in the presence of S9. Within the dose range tested, TEMPO induced reactive oxygen species and decreased glutathione levels in mouse lymphoma cells. In addition, the majority of TEMPO-induced mutants had loss of heterozygosity at the Tk locus, with allele loss of ≤34 Mbp.These results indicate that TEMPO is mutagenic in the MLA and induces micronuclei and hypodiploid nuclei in TK6 cells. Oxidative stress may account for part of the genotoxicity induced by TEMPO in both cell lines.

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“…This coincidence has been well documented by a wealth of independent techniques. (i) The appearance of O 2 in solution was time resolved by four different techniques, namely continuous flow (9), EPR (10,11), polarography with a bare Pt electrode (2,(12)(13)(14) and via absorption changes of intracellular cytochrome c oxidase (15). (ii) The reduction of Y Z ox was detected by timeresolved EPR (10,16,17), and (iii) the reduction of the Mn 4 O x Ca cluster by UV absorption (7,12,(18)(19)(20), delayed chlorophyll fluorescence (DF) (21), and time-resolved Mn-K-edge spectroscopy (8,22).…”

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confidence: 99%

Membrane-inlet mass spectrometry reveals a high driving force for oxygen production by photosystem II

Shevela

Beckmann

Clausen

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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Oxygenic photosynthesis is the basis for aerobic life on earth. The catalytic Mn 4 O x CaY Z center of photosystem II (PSII), after fourfold oxidation, extracts four electrons from two water molecules to yield dioxygen. This reaction cascade has appeared as a single four-electron transfer that occurs in typically 1 ms. Inevitable redox intermediates have so far escaped detection, probably because of very short lifetime. Previous attempts to stabilize intermediates by high O 2 -back pressure have revealed controversial results. Here we monitored by membrane-inlet mass spectrometry (MIMS) the production of 18 O 2 from 18 O-labeled water against a high background of 16 O 2 in a suspension of PSII-core complexes. We found neither an inhibition nor an altered pattern of O 2 production by up to 50-fold increased concentration of dissolved O 2 . Lack of inhibition is in line with results from previous X-ray absorption and visible-fluorescence experiments, but contradictory to the interpretation of previous UV-absorption data. Because we used essentially identical experimental conditions in MIMS as had been used in the UV work, the contradiction was serious, and we found it was not to be resolved by assuming a significant slowdown of the O 2 release kinetics or a subsequent slow conformational relaxation. This calls for reevaluation of the less direct UV experiments. The direct detection of O 2 release by MIMS shows unequivocally that O 2 release in PSII is highly exothermic. Under the likely assumption that one H þ is released in the S 4 → S 0 transition, the driving force at pH 6.5 and atmospheric O 2 pressure is at least 220 meV, otherwise 160 meV.water oxidation | oxygen evolution | isotope-ratio mass spectrometry | bioenergetics O xygenic photosynthesis is the metabolic basis for the most successful forms of life on earth. In cyanobacteria, algae and plants photosystem II (PSII) uses sunlight to split water into dioxygen and reducing equivalents, and it generates proton motive force. The catalytic centre of O 2 production in PSII, coined the OEC (oxygen evolving complex), comprises the manganese-oxygen-calcium (Mn 4 O x Ca) complex and its ligands, which include two substrate "water" molecules of undefined protonation state. It also includes a redox-active tyrosine residue, coined tyrosine ZðY Z Þ, which is the essential electron transfer link to the photoactive reaction center of PSII. Over 40 years ago Kok et al. (1) proposed-on the basis of flash-induced O 2 -evolution patterns (2)-that PSII, clocked and driven by four quanta of light, cycles through five different redox states, named S i (i ¼ 0;…;4), where i is the number of stored oxidizing equivalents. Once four oxidizing equivalents are accumulated O 2 is produced in the spontaneous reaction from S 4 to yield S 0 .In this S i state transition four electrons are transferred from two bound substrate water molecules that were partially or fully deprotonated (m ¼ 0-2) during the S i state cycle. In addition, one or two new substrate water molecules (n ¼ 1;2) bin...

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Measurement of time-resolved oxygen concentration changes in photosynthetic systems by nitroxide-based EPR oximetry

Cited by 38 publications

References 23 publications

Effects of hydrogen/deuterium exchange on photosynthetic water cleavage in PS II core complexes from spinach

Effects of hydrogen/deuterium exchange on photosynthetic water cleavage in PS II core complexes from spinach

Nitroxide TEMPO: A genotoxic and oxidative stress inducer in cultured cells

Membrane-inlet mass spectrometry reveals a high driving force for oxygen production by photosystem II

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