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1.
M. Sang X. -C. Qin W. -D. Wang J. Xie X. -B. Chen K. B. Wang J. -P. Zhang L. -B. Li T. Y. Kuang 《Photosynthetica》2011,49(1):48-54
The generation of superoxide anion radical (O2
·−) in the cytochrome b
6
f complex (Cyt b
6
f) of spinach under high-light illumination was studied using electron paramagnetic resonance spectroscopy. The generation
of O2
·− was lost in the absence of molecular oxygen. It was also suppressed in the presence of NaN3 and could be scavenged by extraneous antioxidants such as ascorbate, β-carotene, and glutathione. The results also indicate that O2
·−, which is produced under high-light illumination of the Cyt b
6
f from spinach, might be generated from a reaction involing 1O2, and the Rieske Fe-S protein could serve as the electron donor in the O2
·− production. The mechanism of photoprotection of the Cyt b
6
f complex by antioxidants is discussed. 相似文献
2.
CHEN XiaoBo ZHAO XiaoHui ZHANG JianPing LI LiangBi & KUANG TingYun 《中国科学:生命科学英文版》2007,50(4):505-510
The singlet excited state lifetime of the chlorophyll a (Chi a) in cytochrome b6f (Cyt b6f) complex was reported to be shorter than that of free Chl a in methanol, but the value was different for Cyt b6f complexes from different sources (~200 and ~600 ps are the two measured results). The present study demonstrated that the singiet excited state lifetime is associated with the detergents n-dodecyl-β-D-maltoside (DDM) and n-octyl-β-D-glucopyranoside (β-OG), but has nothing to do with the different sources of Cyt b6f complexes. Compared with the Cyt b6f dissolved in β-OG, the Cyt b6f in DDM had a lower fluorescence yield, a lower photodegradation rate of Chl a, and a shorter lifetime of Chl a excited state. In short, the singlet excited state lifetime, ~200 ps, of the Chl a in Cyt b6f complex in DDM is closer to the true in vivo. 相似文献
3.
The cytochrome b
6
f (Cyt b
6
f) complex, which functions as a plastoquinol-plastocyanin oxidoreductase and mediates the linear electron flow between photosystem
II (PSII) and photosystem I (PSI) and the cyclic electron flow around PSI, was isolated from spinach (Spinacia oleracea L.) chloroplasts using n-octyl-β-D-glucopyranoside (β-OG). The preparation was also able to catalyze the peroxidase-like reaction in the presence
of hydrogen peroxide (H2O2) and guaiacol. The optimal conditions for peroxidase activity of the preparation included: pH 3.6, ionic strength 0.1, and
temperature 35°C. The apparent Michaelis constant (K
m) values for H2O2 and guaiacol were 50 mM and 2 mM, respectively. The bimolecular rate constant (k
obs) was about 26 M−1 s−1 and the turnover number (K
cat) was about 60 min−1 (20 mM guaiacol, 100 mM sodium phosphate, pH 3.6, 25°C, [H2O2]<100mM). These parameters were similar to those of several other heme-containing proteins, such as myoglobin and Cyt c. 相似文献
4.
The singlet excited state lifetime of the chlorophyll a (Chl a) in cytochrome b
6
f (Cyt b
6
f) complex was reported to be shorter than that of free Chl a in methanol, but the value was different for Cyt b
6
f complexes from different sources (∼200 and ∼600 ps are the two measured results). The present study demonstrated that the
singlet excited state lifetime is associated with the detergents n-dodecyl-β-D-maltoside (DDM) and n-octyl-β-D-glucopyranoside (β-OG), but has nothing to do with the different sources of Cyt b
6
f complexes. Compared with the Cyt b
6
f dissolved in β-OG, the Cyt b
6
f in DDM had a lower fluorescence yield, a lower photodegradation rate of Chl a, and a shorter lifetime of Chl a excited state. In short, the singlet excited state lifetime, ∼200 ps, of the Chl a in Cyt b
6
f complex in DDM is closer to the true in vivo. 相似文献
5.
Fei Ma Xiao-Bo Chen Min Sang Peng Wang Jian-Ping Zhang Liang-Bi Li Ting-Yun Kuang 《Photosynthesis research》2009,100(1):19-28
We have attempted to investigate the correlation between the detergent-perturbed structural integrity of the Cyt b
6
f complex from the marine green alga Bryopsis corticulans and its photo-protective properties, for which the nonionic detergents n-octyl-β-d-glucopyranoside (β-OG) and n-dodecyl-β-d-maltoside (β-DM), respectively, were used for the preparation of Cyt b
6
f, and the singlet oxygen (1O2*) production as well as the triplet excited-state chlorophyll a (3Chl a*) formation and deactivation were examined by spectroscopic means. Near-infrared luminescence of 1O2
* (~1,270 nm) on photo-irradiation was detected for the β-OG preparation where the complex is mainly in oligomeric state, but
not for the β-DM one in which the complex exists in dimeric form. Under anaerobic condition, photo-excitation of Chl a in the β-DM preparation generated 3Chl a* with a lower quantum yield of ΦT ~ 0.02 and a longer lifetime of ~600 μs with respect to those as in the case of β-OG preparation, ΦT ~ 0.12 and 200–300 μs. These results prove that the enzymatically active and intact Cyt b
6
f complex on photo-excitation tends to produce little 3Chl a* or 1O2
*, which implies that the pigment–protein assembly of Cyt b
6
f complex per se is crucial for photo-protection.
F. Ma and X.-B. Chen contributed equally to this work. 相似文献
6.
Quantitative characteristics of photosynthetic electron transport were evaluated in vivo on the basis of the multi-exponential
analysis of OJIP fluorescence transients induced by saturating actinic light. The OJIP fluorescence curve F(t), measured in Chlamydomonas reinhardtii cells, was transformed into the (1 − F
O/F(t)) × (F
V
/F
M)−1 transient, which is shown to relate to PS 2 closure. We assumed that kinetics of PS 2 closure during OJIP rise reflects time-separated
processes related to the establishment of redox equilibrium at the PS 2 acceptor side (OJ), PQ pool (JI), and beyond Cyt b/f
(IP). Three-exponential fitting was applied to (1 − F
O/F(t)) × (F
V
/F
M)−1 transient to obtain lifetimes and amplitudes of the OJ, JI, and IP components of PS 2 closure, which were used to calculate
overall rates of reduction and re-oxidation of the PS 2 acceptor side, PQ pool, and intermediates beyond Cyt b/f complex.
The results, obtained in the presence of inhibitors, oxidative reagents, and under different stress conditions prove the suggested
model and characterize the introduced parameters as useful indicators of photosynthetic function. 相似文献
7.
The CP47 protein was isolated from Photosystem II membranes by using a combination of the detergents n-dodecyl-β-D-maltoside and octyl-β-D-thioglucoside. The purified CP47 was used in a series of crystallization experiments,
which yielded highly reproducible hexagonal crystals. Immunoblot analysis revealed that the isolated CP47 undergoes degradation
even under dim light conditions. This degradation takes place after the protein has been dissociated from the core complex.
Proteolysis experiments with trypsin demonstrated that the dissociation of the CP47 from the PS II core complex results in
changes that render the protein sensitive to proteolysis.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
8.
Yokoyama Eiichi; Murakami Akio; Sakurai Hidehiro; Fujita Yoshihiko 《Plant & cell physiology》1991,32(6):827-834
Stability of thylakoid components under supra-high irradiancewas studied with the cyanophyte Synechocystis PCC 6714. Theactivity of overall photosynthesis was quickly inactivated (T1/2=20min) under supra-high irradiance (300 W m2, white light).In parallel with the inactivation of photosynthesis, QA in PSII was also inactivated. Both inactivations were acceleratedby chloramphenicol (CAP) addition. The reactivation of PS IIrequired weak irradiation and was suppressed by CAP. However,PS I measured as P700 was very stable. The level of PS I measuredas P700 was not significantly reduced by the irradiation for12 h even in the presence of CAP while the level of Cyt b559,component of PS II, was decreased markedly. The function ofPS I before and after supra-high irradiation with CAP was examinedby comparing sizes of P700 oxidation induced by a short flash,by a continuous light, and by determination of O2-and ferredoxin-reduction.No difference was observed in PS I actions before and afterthe irradiation treatment. These results indicate that the PSI complex is very tolerant of supra-high irradiation. However,the cells grown under supra-high irradiance contained much fewerPS I and PS II complexes than Cyt b6f complexes. Theformer levels were reduced to a half to one fourth of thosebefore growth while the level of Cyt b6f complex wasnot reduced so much. A possible mechanism for changes in thylakoidcomposition under supra-high irradiation was discussed. (Received February 16, 1991; Accepted June 12, 1991) 相似文献
9.
Regulation of Photosystem Stoichiometry in the Photosynthetic System of the Cyanophyte Synechocystis PCC 6714 in Response to Light-Intensity 总被引:1,自引:0,他引:1
Light-induced changes in stoichiometry among three thylakoidcomponents, PS I, PS II and Cyt b6-f complexes, were studiedwith the cyanophyte Synechocystis PCC 6714. Special attentionwas paid to two aspects of the stoichiometric change; first,a comparison of the patterns of regulation in response to differencesin light-intensity with those induced by differences in light-quality,and second, the relationship between regulation of the stoichiometryand the steady state of the electron transport system. Resultsfor the former indicated that (1) the abundance of PS I on aper cell basis was reduced under white light at the intensityas high as that for light-saturation of photosynthesis, butPS I per cell was increased under low light-intensity, (2) PSII and Cyt b6-f complexes remained fairly constant, and (3)changes in the abundance of PS I depended strictly on proteinsynthesis. The pattern was identical with that of chromaticregulation. For the second problem, the redox steady-statesof Cyt f and P700 under white light of various intensities weredetermined by flash-spectroscopy. Results indicated that (1)Cyt f and P700 in cells grown under low light-intensity [highratio of PS I to PS II (PS I/PS II)] were markedly oxidizedwhen the cells were exposed to high light-intensity, while theyremained in the reduced state under low light-intensity. (2)After a decrease in the abundance of PS I, most of P700 remainedin the reduced state even under high light-intensity, whilethe level of reduced Cyt f remained low. (3) Both Cyt f andP700 in cells of low PS I/PS II were fully reduced under lowlight-intensity, and Cyt f reduction following the flash wasrapid, which indicates that the turnover of PS I limits theoverall rate of electron flow. After an increase in the abundanceof PS I, the electron transport recovered from the biased state.(4) The redox steady-state of the Cyt b6-f complex correlatedwell with the regulation of PS I/PS II while the state of thePQ pool did not. Based on these results, a working model ofthe regulation of assembly of the PS I complex, in which theredox steady-state of the Cyt b6-f complex is closely relatedto the primary signal, is proposed. (Received August 2, 1990; Accepted December 10, 1990) 相似文献
10.
A pure, active cytochrome b
6
f was isolated from the chloroplasts of the marine green alga, Bryopsis
corticulans. To investigate and characterize this cytochrome b
6
f complex, sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE), absorption spectra measurement and HPLC were employed. It was shown that this purified complex contained four large subunits with apparent molecular masses of 34.8, 24, 18.7 and 16.7 kD. The ratio of Cyt b
6 to Cytf was 2.01 : 1. The cytochromeb
6
f was shown to catalyze the transfer of 73 electrons from decylplastoquinol to plastocyanin–ferricyanide per Cyt f per second. α-Carotene, one kind of carotenoid that has not been found to present in cytochrome b
6
f complex, was discovered in this preparation by reversed phase HPLC. It was different from β-carotene usually found in cytochrome b
6
f complex. The configuration of the major α-carotene component was assigned to be 9-cis by resonance Raman spectroscopy. Different from the previous reports, the configuration of this α-carotene in dissociated state was determined to be all-trans. Besides this carotene, chlorophyll a was also found in this complex. It was shown that the molecular ratios of chlorophylla, cis and all-trans-α-carotene to Cyt f in this complex were 1.2, 0.7 and 0.2, respectively. 相似文献
11.
A series of experiments have been conducted with isolated reaction centers of photosystem two (PS II) with the aim to elucidate the functional role of cytochrome (Cyt b
559). At pH 6.5 it was found that Cyt b
559 was reversibly photoreduced by red actinic light when Mn2+ was present as an electron donor while at pH 8.5 a photo-oxidation was observed under the same lighting conditions, which was dark reversible in the presence of hydroquinone. These pH dependent light induced changes were measured under anaerobic conditions and correlated with changes in the relative levels of high (HP) and low (LP) potential forms of the cytochrome. At pH 6.5 the cytochrome was mainly in its LP form while at pH 8.5 a significant proportion was converted to the HP form as detected by dark titrations with hydroquinone. This pH dependent difference in the levels of HP and LP Cyt b
559 was also detected when bright white light was used to monitor the level of the LP form using a novel reaction involving direct electron donation from the flavin of glucose oxidase (present in the medium and used together with glucose and catalase as an oxygen trap). The results suggest that PS II directly oxidises and reduces the HP and LP forms, respectively and that the extent of these photo-reactions is dependent on the relative levels of the two forms, which are in turn governed by the pH. This conclusion is interpreted in terms of the model presented previously (Barber J and De Las Rivas J (1993) Proc Natl Acad Sci USA 90: 10942–10946) whereby the pH induced effect is considered as a possible mechanism by which interconversion of LP and HP forms of Cyt b
559 is achieved. In agreement with this was the finding that as the extent of photo-oxidisable HPCyt b
559 increases, with increasing pH, the rate of irreversible photo-oxidation of -carotene decreases, a result expected if the HP form protects against donor side photoinhibition.Abbreviations -car
-carotene
- CCCP
carbonylcyanide m-chloro-phenylhydrazone
- Chl
chlorophyll
- Cyt b
559
cytochrome b
559
- HPCyt b
559
high potential form of cytochrome b
559 which is reducible by hydroquinone
- LPCyt b
559
low potential form of cytochrome b
559 which is non-reducible by hydroquinone
- D1 and D2
products of the psbA and psbD genes, respectively
- LHC II
light-harvesting chlorophyll protein complex associated with PS II
- Mes
2-(N-morpholino) ethanesulphonic acid
- P680
primary electron donor of PS II
- Pheo
pheophytin
- PQ
plastoquinone
- PS II
Photosystem II
- QA
first stable quinone electron acceptor of PS II
- QB
second stable quinone electron acceptor of PS II
- RC
reaction center
- SDS
sodium dodecyl sulphate
- SiMo
silicomolybdate
- Tris
tris(hydroxymethyl) amino methane
- YZ and YD
tyrosine residues 161 in D1 and D2 proteins of the PS II RC which act as secondary electron donors to P680 相似文献
12.
Allakhverdieva Y.M. Mamedov M.D. Ferimazova N. Papageorgiou G.C. Gasanov R.A. 《Photosynthetica》1999,36(3):423-432
Glycinebetaine, a compatible osmolyte of halotolerant plants and bacteria, partially protected photosystem (PS) 1 and PS2
electron transport reactions against thermal inactivation but with different efficiencies. In its presence, the temperature
for half-maximal inactivation (t1/2) was generally shifted downward by 3–12 °C. Glycinebetaine stabilized photoinduced oxygen evolving reactions of PS2 by protecting
the tetranuclear Mn cluster and the extrinsic proteins of this complex. A weaker, although noticeable, stabilizing effect
was observed in photoinduced PS2 electron transport reactions that did not originate in the oxygen-evolving complex (OEC).
This weaker protection by glycinebetaine was probably exerted on the PS2 reaction centre. Glycinebetaine protected also photoinduced
electron transport across PS1 against thermal inactivation. The protective effect was exerted on plastocyanin, the mobile
protein in the lumen that carries electrons from the integral cytochrome b
6
f complex to the PS1 complex.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
13.
Rapid and simple isolation of pure photosystem II core and reaction center particles from spinach 总被引:2,自引:2,他引:0
Peter J. van Leeuwen Maaike C. Nieveen Erik Jan van de Meent Jan P. Dekker Hans J. van Gorkom 《Photosynthesis research》1991,28(3):149-153
Pure and active oxygen-evolving PS II core particles containing 35 Chl per reaction center were isolated with 75% yield from spinach PS II membrane fragments by incubation with n-dodecyl--D-maltoside and a rapid one step anion-exchange separation. By Triton X-100 treatment on the column these particles could be converted with 55% yield to pure and active PS II reaction center particles, which contained 6 Chl per reaction center.Abbreviations Bis-Tris
bis[2-hydroxyethyl]imino-tris[hydroxymethyl]methane
- Chl
chlorophyll
- CP29
Chl a/b protein of 29 kDa
- Cyt b
559
cytochrome b
559
- DCBQ
2,5-dichloro-p-benzo-quinone
- LHC II
light-harvesting complex II, predominant Chl a/b protein
- MES
2-[N-Morpholino]ethanesulfonic acid
- Pheo
pheophytin
- PS H
photosystem II
- QA
bound plastoquinone, serving as the secondary electron acceptor in PS II (after Pheo)
- SDS
sodiumdodecylsulfate 相似文献
14.
Effects of NaCl Stress on the Structure,Pigment Complex Composition,and Photosynthetic Activity of Mangrove Bruguiera parviflora Chloroplasts 总被引:7,自引:1,他引:6
Exposure of two-month-old seedlings of Bruguiera parviflora to NaCl stress (0 to 400 mM) for 45 d under hydroponic culture caused notable disorganisation of the thylakoid structure
of chloroplasts in NaCl-treated leaves as revealed from transmission electron microscopy. The absorption spectra of treated
and control thylakoid samples were similar having a red peak at 680 nm and Soret peaks at 439 and 471 nm in the blue region
of the spectrum. The spectra of treated samples differed from control samples by gradual decrease in absorbance of 100, 200,
and 400 mM NaCl treated samples at 471 and 439 nm, which could be due to scattering of radiation in these samples. Thus, absorption
characteristics of thylakoid membranes indicated no major alterations in the structural integrity of the photosynthetic membranes
during salt stress in B. parviflora. Analysis of pigment protein complexes of thylakoids on non-denaturing gel showed that CP1 complex consisting of photosystem
(PS) 1 reaction centre decreased marginally by 19% and the CP47 constituting the core antenna of PS2 declined significantly
by 30% in 400 mM NaCl treated samples in respect to control. This decrease in structural core antenna might cause inefficient
photon harvesting capacity. However, CP43 content did not alter. An increase in CP2/CP1 ratio from 3.2 in control to 4.0 in
400 mM NaCl treated samples indicated significant structural changes in the thylakoids of salt treated plants. Haem staining
of thylakoids revealed significant losses in cytochrome (Cyt)f and Cyt b
6 contents by NaCl stress. However, Cyt b
559 content remained nearly constant in both control and NaCl treated samples. SDS-PAGE of thylakoid proteins showed that the
intensity of many of Coomassie stained polypeptide bands ranging from 15–22 and 28–66 kDa regions decreased significantly
in NaCl treated samples as compared to control. Electron transport activity of thylakoids, measured in terms of DCPIP photoreduction,
was 22% lower in 400 mM NaCl treated plants than in the control ones. Hence, NaCl induces oxidative stress in chloroplasts
causing structural alterations in thylakoids. These structural alterations might be responsible for declined efficiency of
photosystems and reduced electron transport activity.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
15.
By recording leaf transmittance at 820 nm and quantifying the photon flux density of far red light (FRL) absorbed by long-wavelength
chlorophylls of Photosystem I (PS I), the oxidation kinetics of electron carriers on the PS I donor side was mathematically
analyzed in sunflower (Helianthus annuus L.), tobacco (Nicotiana tabacum L.) and birch (Betula pendula Roth.) leaves. PS I donor side carriers were first oxidized under FRL, electrons were then allowed to accumulate on the PS
I donor side during dark intervals of increasing length. After each dark interval the electrons were removed (titrated) by
FRL. The kinetics of the 820 nm signal during the oxidation of the PS I donor side was modeled assuming redox equilibrium
among the PS I donor pigment (P700), plastocyanin (PC), and cytochrome f plus Rieske FeS (Cyt f + FeS) pools, considering
that the 820 nm signal originates from P700+ and PC+. The analysis yielded the pool sizes of P700, PC and (Cyt f + FeS) and associated redox equilibrium constants. PS I density
varied between 0.6 and 1.4 μmol m−2. PS II density (measured as O2 evolution from a saturating single-turnover flash) ranged from 0.64 to 2.14 μmol m−2. The average electron storage capacity was 1.96 (range 1.25 to 2.4) and 1.16 (range 0.6 to 1.7) for PC and (Cyt f + FeS),
respectively, per P700. The best-fit electrochemical midpoint potential differences were 80 mV for the P700/PC and 25 mV for
the PC/Cyt f equilibria at 22 °C. An algorithm relating the measured 820 nm signal to the redox states of individual PS I
donor side electron carriers in leaves is presented. Applying this algorithm to the analysis of steady-state light response
curves of net CO2 fixation rate and 820 nm signal shows that the quantum yield of PS I decreases by about half due to acceptor side reduction
at limiting light intensities before the donor side becomes oxidized at saturating intensities. Footnote:
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
16.
This study was done to confirm our previous observation withthe pattern of changes in electron transport composition inducedby an imbalance of the electron transport state. Contents ofphotosystem (PS) I and II complexes and their antennae and Cytb6/f complex were determined for systems of cyanobacterium SynechocystisPCC 6714 of different PS I/PS II ratios. The results indicatedthat (1) the observed changes in the PS I/PS II ratio are not-dueto regulation of the activities of the respective PS's but tochanges in their contents, (2) the molar ratio between PS IIand Cyt b6/f complexes was fairly constant when marked changesoccurred in the PS I content, and (3) the PS II and Cyt b6/fcontents per cell remained fairly constant while the PS I contentchanged markedly. These findings agree with our previous observationwith autotrophic cells of Anacystis nidulans Tx 20 and supportour argument that in cyanobacterial and red algal electron transportsystems, the content of the terminalcomponent(s), such as PSI complex, is regulated in order to maintain a balance betweenthe electron influx by PS II action to the system and the effluxby PS I action from it. (Received June 3, 1987; Accepted September 20, 1987) 相似文献
17.
Begoña Gómez-Miranda Alicia Prieto Juan Antonio Leal Oussama Ahrazem Jesús Jiménez-Barbero Manuel Bernabé 《Glycoconjugate journal》2003,20(4):239-246
The alkali extractable and water-soluble cell wall polysaccharides F1SS from Aspergillus wentii and Chaetosartorya chrysella have been studied by methylation analysis, 1D- and 2D-NMR, and MALDI-TOF analysis. Their structures are almost identical,
corresponding to the following repeating unit:
[→ 3)-β-D-Galf-(1 → 5)-β-D-Galf-(1 →]
n
→ mannan core.
The structure of this galactofuranose side chain differs from that found in the pathogenic fungus Aspergillus fumigatus, in other Aspergillii and members of Trichocomaceae:
[→ 5)-β-D-Galf-(1 →]
n
→ mannan core.
The mannan cores have also been investigated, and are constituted by a (1 → 6)-α-mannan backbone, substituted at positions
2 by chains from 1 to 7 residues of (1 → 2) linked α-mannopyranoses. Published in 2004.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
18.
Agu Laisk Eero Talts Vello Oja Hillar Eichelmann Richard B. Peterson 《Photosynthesis research》2010,103(2):79-95
Fast cyclic electron transport (CET) around photosystem I (PS I) was observed in sunflower (Helianthus annuus L.) leaves under intense far-red light (FRL) of up to 200 μmol quanta m−2 s−1. The electron transport rate (ETR) through PS I was found from the FRL-dark transmittance change at 810 and 950 nm, which
was deconvoluted into redox states and pool sizes of P700, plastocyanin (PC) and cytochrome f (Cyt f). PC and P700 were in
redox equilibrium with K
e = 35 (ΔE
m = 90 mV). PS II ETR was based on O2 evolution. CET [(PS I ETR) − (PS II ETR)] increased to 50–70 μmol e− m−2 s−1 when linear electron transport (LET) under FRL was limited to 5 μmol e− m−2 s−1 in a gas phase containing 20–40 μmol CO2 mol−1 and 20 μmol O2 mol−1. Under these conditions, pulse-saturated fluorescence yield F
m was non-photochemically quenched; however, F
m was similarly quenched when LET was driven by low green or white light, which energetically precluded the possibility for
active CET. We suggest that under FRL, CET is rather not coupled to transmembrane proton translocation than the CET-coupled
protons are short-circuited via proton channels regulated to open at high ΔpH. A kinetic analysis of CET electron donors and
acceptors suggests the CET pathway is that of the reversed Q-cycle: Fd → (FNR) → Cyt cn → Cyt bh → Cyt bl → Rieske FeS → Cyt f → PC → P700 →→ Fd. CET is activated when PQH2 oxidation is opposed by high ΔpH, and ferredoxin (Fd) is reduced due to low availability of e− acceptors. The physiological significance of CET may be photoprotective, as CET may be regarded as a mechanism of energy
dissipation under stress conditions. 相似文献
19.
From a heterotrophic bacterium,Xanthomonas sp. DY44 which was previously reported to oxidize hydrogen sulfide (H2S) to polysulfide, cytochromec-555 (cyt.c-555) responsible for oxidation of sulfide was purified by DEAE-Toyopearl and Sepadex G-75 column chromatography. Cyt.c-555 with a molecular weight of 12,500 showed maximum absorption at 555 nm (α-peak), 522 nm (β-peak) and 417 nm (γ-peak) for
the reduced form which was prepared by addition of Na2S2O4. Cyt.c-555 was also reduced by addition of sulfide (Na2S and H2S), and the oxidized products of sulfide by cyt.c-555 was identified as polysulfide. The reduced form of cyt.c-555 was suggested to be oxidized coupled with cyt.c oxidase which is tolerant to sulfide. 相似文献
20.
In this study, the release of mitochondrial proapoptotic intermembrane space proteins induced by ex-ogenous C2-ceramide in human colon carcinoma (HT-29) cell line was investigated. HT-29 cells were treated with 12.5, 25 and 50 μmol/L C2-ceramide in vitro. Flow cytometer was used to detect the mito-chondrial membrane potential (ΔΨm). Subcellular fractions were extracted by Mitochondrial/Cytosol Fractionation Kit after C2-ceramide treatment for 24 h. SDS-PAGE was used to determine the level of cytochrome c (Cyt c), high temperature requirement A2 (HtrA2) and second mitochondrial-derived ac-tivator of caspases (Smac) released from mitochondria, the expression of X-linked inhibitor of apop-tosis protein (XIAP) and caspase-3 for 24 h. The results showed that ΔΨm began to decrease from 6 h after 25 and 50 μmol/L C2-ceramide treatment (P<0.05) and cyclosporin A (CsA) could inhibit the col-lapse of ΔΨm through regulating mitochondrial membrane permeability transition pore. There was no effect of C2-ceramide on the expression of Cyt c, HtrA2 and Smac in the total levels. 12.5, 25 and 50 μmol/L C2-ceramide could induce Cyt c, HtrA2 and Smac to release from mitochondria to cytosol and down-regulate the expression of XIAP (P<0.05). Also there was expression of cleaved caspase-3 with C2-ceramide treatment. After the treatment with caspase inhibitor, C2-ceramide still induced the release of Cyt c and HtrA2, but Smac did not. Therefore, C2-ceramide could induce apoptosis of HT-29 cells through the mitochondria pathway. The release of Cyt c, HtrA2 and Smac from mitochondria did not occur via the same mechanism, the release of Cyt c and HtrA2 was caspase-independent and the re-lease of Smac was caspase-dependent. 相似文献