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1.
Redox titrations of the photo-induced pheophytin EPR signal in Photosystem II show two transitions which reflect the redox state of Q. The high potential wave (Em ? ?50 mV) can be photo-induced at 5 K and 77 K. The low potential wave (Em ? ?275 mV) required illumination at 200 K. This indicates the presence of two kinds of PS-II reaction centres differing in terms of the competence of their donors at low temperature and the Em-values of their acceptors. Measurements of the semiquinone-iron acceptor also demonstrate functional heterogeneity at low temperature. This is the first observation of the semiquinone-iron acceptor in a non-mutant species. 相似文献
2.
N. Murata S. Araki Y. Fujita K. Suzuki T. Kuwabara P. Mathis 《Photosynthesis research》1986,9(1-2):63-70
Pheophytin and chlorophyll extracted from oxygen-evolving photosystem II particles, chloroplast thylakoids and cyanobacterial cells were separated by column chromatography with DEAE-Toyopearl, and quantitatively determined by spectrophotometry. The molecular ratio of chlorophyll a+b to pheophytin a was about 100 in spinach photosystem II particles and about 140 in spinach thylakoids. Using flash spectrophotometry of P680 and measurement of flash-induced oxygen yield, the molecular ratio of the chlorophyll to the photochemical reaction center II was determined to be about 200 in the photosystem II particles. These findings suggest that the stoichiometry in photosystem II particles is one reaction center II and two pheophytin a molecules per about 200 chlorophyll molecules. The same stoichiometry for pheophytin to the reaction center II was obtained in the cyanobacteria, Anacystis nidulans and Synechocystis PCC 6714. A quantitative determination of pheophytin a and the electron donor P700 in stroma thylakoids from pokeweed suggests that photosystem I does not contain pheophytin.Dedicated to Prof. L.N.M. Duysens on the occasion of his retirement. 相似文献
3.
To investigate the effects of a membrane potential on excitation trapping and charge separation in Photosystem II we have studied the chlorophyll fluorescence yield in osmotically swollen chloroplasts subjected to electrical field pulses. Significant effects were observed only in those membrane regions where a large membrane potential opposing the photochemical charge separation was built up. When the fluorescence yield was low, close to F0, a much higher yield, up to Fmax, was observed during the presence of the membrane potential. This is explained by an inhibition by the electrical field of electron transfer to the quinone acceptor Q, resulting in a decreased trapping of excitations. A field pulse applied when the fluorescence yield was high, Q and the donor side being in the reduced state, had the opposite effect: the fluorescence was quenched nearly to F0. This field-induced fluorescence quenching is ascribed to reversed electron transfer from Q? to the intermediate acceptor, pheophytin. Its field strength dependence suggests that the midpoint potential difference between pheophytin and Q is at most about 300 mV. Even then it must be assumed that electron transfer between pheophytin and Q spans 90% of the potential difference across the membrane. 相似文献
4.
We have measured the flash-induced absorbance difference spectrum attributed to the formation of the secondary radical pair, P+Q−, between 270 nm and 1000 nm at 77 K in photosystem II of the chlorophyll d containing cyanobacterium, Acaryochloris marina. Despite the high level of chlorophyll d present, the flash-induced absorption difference spectrum of an approximately 2 ms decay component shows a number of features which are typical of the difference spectrum seen in oxygenic photosynthetic organisms containing no chlorophyll d. The spectral shape in the near-UV indicates that a plastoquinone is the secondary acceptor molecule (QA). The strong C-550 change at 543 nm confirms previous reports that pheophytin a is the primary electron acceptor. The bleach at 435 nm and increase in absorption at 820 nm indicates that the positive charge is stabilized on a chlorophyll a molecule. In addition a strong electrochromic band shift, centred at 723 nm, has been observed. It is assigned to a shift of the Qy band of the neighbouring accessory chlorophyll d, ChlD1. It seems highly likely that it accepts excitation energy from the chlorophyll d containing antenna. We therefore propose that primary charge separation is initiated from this chlorophyll d molecule and functions as the primary electron donor. Despite its lower excited state energy (0.1 V less), as compared to chlorophyll a, this chlorophyll d molecule is capable of driving the plastoquinone oxidoreductase activity of photosystem II. However, chlorophyll a is used to stabilize the positive charge and ultimately to drive water oxidation. 相似文献
5.
Chemeris Yu. K. Korol'kov N. S. Seifullina N. Kh. Rubin A. B. 《Russian Journal of Plant Physiology》2004,51(4):435-441
A prolonged (20 h) dark incubation of Chlorella pyrenoidosa algae at 37°C resulted in a twofold rise of the slowly rising phase (10–15 min), sF
v, in the kinetics of variable chlorophyll fluorescence, F
v (F
v = F
m – F
0) in diuron-treated cells. This effect suggests the accumulation of inactive photosystem II (PSII) complexes with low efficiency of primary quinone acceptor of electron of PSII (QA) reduction. The presence of methylamine (MA), a thylakoid membrane uncoupler, or N, N-dicyclohexylcarbodiimide, an inhibitor of ATPase, precluded the accumulation of inactive PSII complexes. When salicylhydroxamate promoted the reduction of the plastoquinone (PQ) pool, exogenous ATP accelerated the accumulation of inactive complexes. Dark PQ oxidation in the presence of nonmetabolized glucose analog, 2-deoxy-D-glucose, lowered the content of inactive PSII complexes, and NaF, an inhibitor of chloroplast phosphatases, retarded this process. These data are considered as evidence for a mechanism regulating the content of inactive PSII complexes in the process of redox-dependent phosphorylation of D1- and/or D2-proteins of PSII. 相似文献
6.
The effect of high light on the acceptor side of photosystem II of chloroplasts and core particles of spinach was studied.
BothV
max and apparentK
m for DCIP were altered in photoinhibited photosystem II core particles. The double reciprocal plot analysis as a function
of actinic light showed increased slope in chloroplasts photoinhibited in the presence of DCMU. Exposure of chloroplasts to
high light in the presence of DCMU did not protect the chloroplast against high light induced decrease in Fm, level. Further the high light stress induced decrease inF
m level was not restored by the addition of DCMU. These results suggest that the high light stress induced damage to chloroplast
involves alteration in the binding site forQ
B on the DI protein on the acceptor side of photosystem II 相似文献
7.
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
8.
The photoacoustic (PA) characteristics (energy storage and heat dissipation) of photosystem II (PSII) core-enriched particles from barley were studied (i) in conditions where there was electron flow, i.e., in the presence of a combination of the electron acceptor K3 Fe (CN)6, referred to as FeCN, and the electron donor diphenylcarbazide (DPC), and (ii) in conditions where electron flow was suppressed, i.e., in the absence of FeCN and DPC. The experimental data show that a decrease of heat dissipation with a minimum at 540 nm can be interpreted as energy storage resulting from the presence of pheophytin (Pheo) in the PSII particles. On account of the capability of the PA method to measure the energy absorbed by the chromophores which is converted to heat, it is suggested that the PA detection of Pheo present in the PSII complex will permit to clarify the function of processes involving non-radiative relaxation of excited states in P680-Pheo-QA interactions.Abbreviations -Car
-Carotene
- Chl
Chlorophyll
- DPC
Diphenylcarbazide
- EPR
Electron Paramagnetic Resonance
- FeCN
potassium ferricyanide
- HEPES
N-2-hydroxyethylenepiperazine-N-2-ethanesulfonate
- P680
reaction center of PSII
- PA
Photoacoustic
- Pheo
pheophytin
- PSI
photosystem I
- PSII
photosystem II
- QA
primary electron acceptor of PSII 相似文献
9.
The suggestion that the electron acceptor A1 in plant photosystem I (PSI) is a quinone molecule is tested by comparisons with the bacterial photosystem. The electron spin polarized (ESP) EPR signal due to the oxidized donor and reduced quinone acceptor (P
870
+
Q-) in iron-depleted bacterial reaction centers has similar spectral characteristics as the ESP EPR signal in PSI which is believed to be due to P
700
+
A
1
-
, the oxidized PSI donor and reduced A1. This is also true for better resolved spectra obtained at K-band (24 GHz). These same spectral characteristics can be simulated using a powder spectrum based on the known g-anisotropy of reduced quinones and with the same parameter set for Q- and A1
-. The best resolution of the ESP EPR signal has been obtained for deuterated PSI particles at K-band. Simulation of the A1
- contribution based on g-anisotropy yields the same parameters as for bacterial Q- (except for an overall shift in the anisotropic g-factors, which have previously been determined for Q-). These results provide evidence that A1 is a quinone molecule. The electron spin polarized signal of P700
+ is part of the better resolved spectrum from the deuterated PSI particles. The nature of the P700
+ ESP is not clear; however, it appears that it does not exhibit the polarization pattern required by mechanisms which have been used so far to explain the ESP in PSI.Abbreviations hf
hyperfine
- A0
A0 acceptor of photosystem I
- A1
A1 acceptor of photosystem I
- Brij-58
polyoxyethylene 20 cetyl ether
- CP1
photosystem I particles which lack ferridoxin acceptors
- ESP
electron spin polarized
- EPR
electron paramagnetic resonance
- I
intermediary electron acceptor, bacteriopheophytin
- LDAO
lauryldimethylamine
- N-oxide, P700
primary electron donor of photosystem I
- PSI
photosystem I
- P700
T
triplet state of primary donor of photosystem I
- P870
primary donor in R. sphaeroides reaction center
- Q
quinore-acceptor in photosynthetic bacteria
- RC
reaction center 相似文献
10.
Discovery of pheophytin function in the photosynthetic energy conversion as the primary electron acceptor of Photosystem II 总被引:2,自引:2,他引:0
Klimov VV 《Photosynthesis research》2003,76(1-3):247-253
This minireview describes the discovery of participation of pheophytin, a metal-free derivative of chlorophyll, in the early
steps of photosynthetic solar energy conversion as the primary electron acceptor of Photosystem II.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
11.
Redox titrations of the flash-induced formation of C550 (a linear indicator of Q?) were performed between pH 5.9 and 8.3 in Chlamydomonas Photosystem II particles lacking the secondary electron acceptor, B. One-third of the reaction centers show a pH-dependent midpoint potential (Em,7.5) = ? 30 mV) for redox couple , which varies by ?60 mV/pH unit. Two-thirds of the centers show a pH-independent midpoint potential (Emm = + 10 mV) for this couple. The elevated pH-independent Em suggests that in the latter centers the environment of Q has been modified such as to stabilize the semiquinone anion, Q?. The midpoint potentials of the centers having a pH-dependent Em are within 20 mV of those observed in chloroplasts having a secondary electron acceptor. It appears therefore that the secondary electron acceptor exerts little influence on the Em of . An EPR signal at g 1.82 has recently been attributed to a semiquinone-iron complex which comprises Q?. The similar redox behavior reported here for C550 and reported by others (Evans, M.C.W., Nugent, J.H.A., Tilling, L.A. and Atkinson, Y.E. (1982) FEBS Lett. 145, 176–178) for the g 1.82 signal in similar Photosystem II particles confirm the assignment of this EPR signal to Q?. At below ?200 mV, illumination of the Photosystem II particles produces an accumulation of reduced pheophytin (Ph?). At ?420 mV Ph? appears with a quantum yield of 0.006–0.01 which in this material implies a lifetime of 30–100 ns for the radical pair P-680+Ph?. 相似文献
12.
Oxygen evolving photosystem II particles were exposed to 100 and 250 W m–2 white light at 20°C under aerobic, anaerobic and strongly reducing (presence of dithionite) conditions. Three types of photoinactivation processes with different kinetics could be distinguished: (1) The fast process which occurs under strongly reducing (t
1/21–3 min) and anaerobic conditions (t
1/24–12 min). (2) The slow process (t
1/215–40 min) and (3) the very slow process (t
1/2>100 min), both of which occur under all three sets of conditions.The fast process results in a parallel decline of variable fluorescence (F
v) and of Hill reaction rate, accompanied by an antiparallel increase of constant fluorescence (F
o). We assume that trapping of QA in a negatively charged stable state, (QA
–)stab, is responsible for the effects observed.The slow process is characterized by a decline of maximal fluorescence (F
m). In presence of oxygen this decline is due to the well known disappearance of F
v which proceeds in parallel with the inhibition of the Hill reaction; F
o remains essentially constant. Under anaerobic and reducing conditions the decline of F
m represents the disappearance of the increment in F
o generated by the fast process. We assume that the slow process consists in neutralization of the negative charge in the domain of QA in a manner that renders QA non-functional. The charge separation in the RC is still possible, but energy of excitation becomes thermally dissipated.The very slow photoinactivation process is linked to loss of charge separation ability of the PS II RC and will be analyzed in a forthcoming paper.Abbreviations
F
chlorophyll a fluorescence
-
F
o, F
v, F
m
constant, variable, maximum fluorescence
-
F
o, F
v, F
m
the same, measured in presence of dithionite (F
v suppression method)
- PS II
photosystem II
- RC
reaction centre (P680. Pheo)
- P680
primary electron donor
- Pheo
pheophytin, intermediary electron acceptor
- QA, QB
the primary and secondary electron acceptor
- Z, D
electron donors to P680
- (QA)stab, (QA H)stab
hypothetical modifications of QA resulting from photoinactivation
- O-, A- and R-conditions
aerobic, anaerobic and strongly reducing (presence of dithionite) conditions
- MES
2-(N-morpholine) ethanesulphonic acid
- DCPIP
2,6-dichlorphenolindophenol
- GGOC
mixture of glucose, glucose oxidase and catalase
- DT-20
oxygen-evolving PS II particles 相似文献
13.
Nikitishena OV Smolova TN Khatypov RA Shkuropatov AJ Klimov VV 《Biochemistry. Biokhimii?a》2002,67(3):364-371
A new pathway of photoinactivation of photosystem II (PS II) connected with irreversible photoaccumulation of reduced pheophytin (Ph) in isolated D1–D2–cytochrome b
559 complexes of reaction center (RC) of PS II was discovered. The inhibitory effects of white light illumination on photochemical activity of D1–D2–cytochrome b
559 complexes of RCs of photosystem II, isolated from pea chloroplasts, have been compared under anaerobic conditions in the absence and in the presence of sodium dithionite, electron transfer from which to the oxidized primary electron donor P680+ results in the photoaccumulation of anion-radical of the primary electron acceptor, PH. In both cases, prolonged illumination (1-5 min, 120 W/m2) led to a pronounced loss of the photochemical activity as it was monitored by measuring the amplitude of the reversible photoinduced absorbance changes at 682 nm related to the photoreduction of Ph. The extent of the photoinactivation depended on the illumination time and pH of the medium. At pH 8.0, the presence of dithionite during photoinactivation brought about a protective effect compared to that in a control sample. In contrast, lowering pH to 6.0 increased the sensitivity to photoinactivation in the dithionite containing samples. For 5 min irradiation, the photochemical activity in the absence and in the presence of dithionite decreased by 35 and 72%, respectively (this was accompanied by an irreversible bleaching of the pheophytin Qx absorption band at 542 nm). Degradation of the D1 and D2 proteins was not observed under these conditions. A subsequent addition of an electron acceptor, potassium ferricyanide, to the illuminated samples restored neither the amplitude of the signal at 682 nm nor absorption at 542 nm. It is suggested that at pH < 7.0 the photoaccumulated PH is irreversibly converted into a secondary, most probably protonated form, that does not lead to destruction of the RCs but prevents the photoformation of the primary radical pair [P680+PH]. A possible application of this effect to photoinactivation of PS II in vivo is discussed. 相似文献
14.
In order to characterize the photosystem II (PS II) centers which are inactive in plastoquinone reduction, the initial variable fluorescence rise from the non-variable fluorescence level Fo to an intermediate plateau level Fi has been studied. We find that the initial fluorescence rise is a monophasic exponential function of time. Its rate constant is similar to the initial rate of the fastest phase (-phase) of the fluorescence induction curve from DCMU-poisoned chloroplasts. In addition, the initial fluorescence rise and the -phase have the following common properties: their rate constants vary linearly with excitation light intensity and their fluorescence yields are lowered by removal of Mg++ from the suspension medium. We suggest that the inactive PS II centers, which give rise to the fluorescence rise from Fo to Fi, belong to the -type PS II centers. However, since these inactive centers do not display sigmoidicity in fluorescence, they thus do not allow energy transfer between PS II units like PS II.Abbreviations DCMU
3-(3,4-dichlorophenyl)-1,1-dimethyl urea
- DMQ
2,5-dimethyl-p-benzoquinone
- Fo
initial non-variable fluorescence yield
- Fm
maximum fluorescence yield
- Fi
intermediate fluorescence yield
- PS II
photosystem II
- QA
primary quinone acceptor of PS II
- QB
secondary quinone acceptor of PS II 相似文献
15.
When the photosystem II quinone acceptor complex has been singly reduced to the state QAQ?B, there is a 22 s half-time back-reaction of Q?B with an oxidized photosystem II donor (S2), directly measured here for the first time. From the back-reaction kinetics with and without inhibitors, kinetic and equilibrium parameters have been estimated. We suggest that the state QAQ?B of the complex is formed by a second-order reaction of vacant reaction centers in the state Q?A with plastoquinone from the pool, and discuss the physico-chemical parameters involved. 相似文献
16.
17.
The reversible inhibition of Photosystem II by salicylaldoxime was studied in spinach D-10 particles by fluorescence, optical absorption, and electron spin resonance spectroscopy. In the presence of 15 mM salicylaldoxime, the initial fluorescence yield was raised to the level of the maximum fluorescence, indicating efficient charge recombination between reduced pheophytin (Ph) and P680+. In agreement with the rapid (ns) backreaction expected between Ph– and P680+, the optical absorption transient at 820 mm was not observed. When the particles were washed free of salicylaldoxime, the optical absorption transient resulting from the rereduction of P680+ was restored to the µs timescale. These results, along with the previously observed inhibition of electron transport reactions and diminution of the 515-nm absorption change in chloroplasts [Golbeck, J.H. (1980) Arch Biochem Biophys 202, 458–466], are consistent with a site of inhibition between Ph and QA in Photosystem II. ESR Signal IIf and Signal Its were abolished in the presence of 25 mM salicylaldoxime, but both signals could be recovered by washing the D-10 particles free of the inhibitor. The loss of Signal Ilf is most likely a consequence of the inhibition between Ph and QA; the rapid charge recombination between Ph– and P680+ would preclude electron transfer from an electron donor on the oxidizing side of Photosystem II. The loss of Signal Its may be due to a change in the environment of the donor complex such that the semiquinone radical giving rise to Signal Its interacts with a nearby reductant.Abbreviations D1
electron donor to P680+ in oxygen-inhibited chloroplasts
- DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- F0
prompt chlorophyll a fluorescence yield
- Fi
initial chlorophyll a fluorescence yield
- Fmax
maximum chlorophyll a fluorescence yield
- Fvar
variable chlorophyll a fluorescence yield
- FWHM
full width at half maximum
- Mes
2-(N-morpholino) ethanesulfonic acid
- P680
reaction center chlorophyll a of photosystem II
- Ph
pheophytin intermediate electron acceptor
- QA
primary quinone electron acceptor
- QB
secondary quinone electron acceptor
- Tris
tris(hydroxymethyl)aminomethane
- Z
electron donor to P680+ 相似文献
18.
Photosystem I particles devoid of the secondary electron acceptor A1 were studied by nanosecond flash absorption. The primary radical pair (P-700+, A0
-) decays with a half-time of 35 ns. The difference spectrum was measured (400–870 nm). After subtraction of the P-700+/P-700 difference spectrum, the A0
-/A0 was obtained. It includes bleachings centered at 690 and 430 nm, and broad positive bands in the near infra-red and the blue-green. This spectrum is consistent with A0 being chlorophyll a absorbing at 690 nm. 相似文献
19.
《BBA》1985,808(2):343-347
Photosystem II particles prepared according to Berthold et al. (Berthold, D.A., Babcock, G.T. and Yocum. C.F. (1981) FEBS Lett. 134, 231–234) and to Ganago and Klimov (Ganago, I.B. and Klimov, V.V. (1985) Biofizika, in the press) were subjected to an iron extraction procedure and cooled in the light under reducing conditions. The samples showed a 0.9 mT wide EPR line at g = 2.0044 attributed to the reduced primary acceptor Q−A. Further prolonged illumination at 15 K generated a wide, somewhat asymmetric EPR signal at g = 2.0034−2.0038 that showed strong, reversible polarization upon continuous illumination at 15 K and below. The signal is ascribed to an acceptor that becomes spin-polarized through exchange-mediated transfer of polarization as described previously for photosynthetic bacteria (Gast, P. and Hoff, A.J. (1979) Biochim. Biophys. Acta 548, 502–535). Arguments are given that the aceptor may be intermediate between the pheophytin transient acceptor and QA. 相似文献
20.
The recent crystal structure of photosystem I (PSI) from Thermosynechococcus elongatus shows two nearly symmetric branches of electron transfer cofactors including the primary electron donor, P700, and a sequence of electron acceptors, A, A0 and A1, bound to the PsaA and PsaB heterodimer. The central magnesium atoms of each of the putative primary electron acceptor chlorophylls, A0, are unusually coordinated by the sulfur atom of methionine 688 of PsaA and 668 of PsaB, respectively. We [Ramesh et al. (2004a) Biochemistry 43:1369-1375] have shown that the replacement of either methionine with histidine in the PSI of the unicellular green alga Chlamydomonas reinhardtii resulted in accumulation of A0− (in 300-ps time scale), suggesting that both the PsaA and PsaB branches are active. This is in contrast to cyanobacterial PSI where studies with methionine-to-leucine mutants show that electron transfer occurs predominantly along the PsaA branch. In this contribution we report that the change of methionine to either leucine or serine leads to a similar accumulation of A0− on both the PsaA and the PsaB branch of PSI from C. reinhardtii, as we reported earlier for histidine mutants. More importantly, we further demonstrate that for all the mutants under study, accumulation of A0− is transient, and that reoxidation of A0− occurs within 1-2 ns, two orders of magnitude slower than in wild type PSI, most likely via slow electron transfer to A1. This illustrates an indispensable role of methionine as an axial ligand to the primary acceptor A0 in optimizing the rate of charge stabilization in PSI. A simple energetic model for this reaction is proposed. Our findings support the model of equivalent electron transfer along both cofactor branches in Photosystem I. 相似文献