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1.
In this article, the three-dimensional structures of photosynthetic reaction centers (RCs) are presented mainly on the basis of the X-ray crystal structures of the RCs from the purple bacteria Rhodopseudomonas (Rp.) viridis and Rhodobacter (Rb.) sphaeroides. In contrast to earlier comparisons and on the basis of the best-defined Rb. sphaeroides structure, a number of the reported differences between the structures cannot be confirmed. However, there are small conformational differences which might provide a basis for the explanation of observed spectral and functional discrepancies between the two species.A particular focus in this review is on the binding site of the secondary quinone (QB), where electron transfer is coupled to the uptake of protons from the cytoplasm. For the discussion of the QB site, a number of newlydetermined coordinate sets of Rp. viridis RCs modified at the QB site have been included. In addition, chains of ordered water molecules are found leading from the cytoplasm to the QB site in the best-defined structures of both Rp. viridis and Rb. sphaeroides RCs.Abbreviations BA
accessory bacteriochlorophyll in the active branch
- BB
accessory bacteriochlorophyll in the inactive branch
- D
primary electron donor (special pair)
- DL
special pair bacteriochorophyll bound by the L subunit
- DM
special pair bacteriochorophyll bound by the M subunit
- QA
primary electron acceptor quinone
- QB
secondary electron acceptor quinone
- RC
reaction center
-
Rb.
Rhodobacter
-
Rp.
Rhodopseudomonas
- A
bacteriopheophytin in the active branch
- B
bacteriopheophytin in the inactive branch 相似文献
2.
Hans Rudolf Bosshard Mario Snozzi Reinhard Bachofen 《Journal of bioenergetics and biomembranes》1987,19(4):375-382
Mitochondrial cytochromec (horse), which is a very efficient electron donor to bacterial photosynthetic reaction centersin vitro, binds to the reaction center ofRhodospirillum rubrum with an approximate dissociation constant of 0.3–0.5 µM at pH 8.2 and low ionic strength. The binding site for the reaction center is on the frontside of cytochromec which is the side with the exposed heme edge, as revealed by differential chemical acetylation of lysines of free and reaction-center-bound cytochromec. In contrast, bacterial cytochromec
2 was found previously to bind to the detergent-solubilized reaction center through its backside, i.e., the side opposite to the heme cleft [Rieder, R., Wiemken, V., Bachofen, R., and Bosshard, H. R. (1985).Biochem. Biophys. Res. Commun.
128, 120–126]. Binding of mitochondrial cytochromec but not of mitochondrial cytochromec
2 is strongly inhibited by low concentrations of poly-l-lysine. The results are difficult to reconcile with the existence of an electron transfer site on the backside of cytochromec
2. 相似文献
3.
The influence of growth rate, the presence of acetate and variation in the dissolved oxygen concentration on the kinetics
of nitrite oxidation was studied in suspensions of intact cells of Nitrobacter winogradskyi and Nitrobacter hamburgensis. The cells were grown in nitrite-limited chemostats at different dilution rates under chemolithotrophic and mixotrophic conditions.
Growth of N. hamburgensis in continuous culture was dependent on the presence of acetate. Acetate hardly affected the maximal nitrite oxidation rate
per cell (V
max), but displayed a distinctly negative effect on the saturation constants for nitrite oxidation (K
m
) of both Nitrobacter species. This effect was reversible; when acetate was removed from the suspensions the K
m
-values for nitrite oxidation returned to their original values.
A reduction of the dissolved oxygen concentration from 100% to 18% air saturation slightly decreased the V
max of chemolithotrophically grown N. winogradskyi cells, whereas a 2.3 fold increase was observed with mixotrophically grown cells of N. hamburgensis. It is suggested that the large variation in K
m
encountered in field samples could be due to this observed phenotypic variability. The V
max per cell is not a constant, but apparently is dependent on growth rate and environmental conditions. This implies that potential
nitrite oxidation activity and numbers of cells are not necessarily related. Considering their kinetic characteristics, it
is unlikely that N. hamburgensis is able to compete succesfully with N. winogradskyi for limiting amounts of nitrite under mixotrophic conditions. However, at reduced partial oxygen tensions, N. hamburgensis may become the better competitor. 相似文献
4.
Andrew T. Poole John J. Ross Naomi L. Lawrence James B. Reid 《Plant Growth Regulation》1995,16(3):257-262
Gibberellin A4 (GA4) was identified for the first time in the garden pea (Pisum sativum) L.), by gas chromatography-mass spectrometry. However, in wild-type shoots the level of GA4 was only about 6% of the level of GA1, and it is therefore unlikely that GA4 plays a major role per se in the control of pea stem elongation. In shoots of the le mutant, GA4 was not detected, while the level of GA9 was approximately twice that found in the wild-type. The le mutation also markedly reduced the elongation response to applied GA9. It appears, therefore, that in Pisum the le mutation blocks the 3-hydroxylation of GA9 to GA4, in addition to the 3-hydroxylation of GA20 to GA1. In contrast, the le mutation did not reduce the response to applied GA5, suggesting the step GA5 to GA3 is not catalysed by the enzyme controlled by the Le gene. The step GA5 to GA3 was confirmed in peas by metabolite analysis after treatment with deuterated GA5. 相似文献
5.
An important issue in theoretical epidemiology is the epidemic thresholdphenomenon, which specify the conditions for an epidemic to grow or die out.In standard (mean-field-like) compartmental models the concept of the basic reproductive number, R
0, has been systematically employed as apredictor for epidemic spread and as an analytical tool to study thethreshold conditions. Despite the importance of this quantity, there are nogeneral formulation of R
0 when one considers the spread of a disease ina generic finite population, involving, for instance, arbitrary topology ofinter-individual interactions and heterogeneous mixing of susceptible andimmune individuals. The goal of this work is to study this concept in ageneralized stochastic system described in terms of global and localvariables. In particular, the dependence of R
0 on the space ofparameters that define the model is investigated; it is found that near ofthe `classical' epidemic threshold transition the uncertainty about thestrength of the epidemic process still is significantly large. Theforecasting attributes of R
0 for a discrete finite system is discussedand generalized; in particular, it is shown that, for a discrete finitesystem, the pretentious predictive power of R
0 is significantlyreduced. 相似文献
6.
Susan M. Howitt Andrew J. W. Rodgers Lyndall P. Hatch Frank Gibson Graeme B. Cox 《Journal of bioenergetics and biomembranes》1996,28(5):415-420
F0F1-ATPase structural information gained from X-ray crystallography and electron microscopy has activated interest in a rotational mechanism for the F0F1-ATPase. Because of the subunit stoichiometry and the involvement of both thea- andc-subunits in the mechanism of proton movement, it is argued that relative movement must occur between the subunits. Various options for the arrangement and structure of the subunits involved are discussed and a mechanism proposed. 相似文献
7.
Petronio Pasquali Mauro Degli Esposti Laura Landi Luciana Cabrini Giorgio Lenaz 《Journal of bioenergetics and biomembranes》1985,17(5):283-294
Depletion of endogenous ubiquinone by pentane extraction of mitochondrial membranes lowered succinate-ferricyanide reductase activity, whereas quinone reincorporation restored the enzymatic activity as well as antimycin sensitivity. The oxidant-induced cytochromeb extrareduction, normally found upon ferricyanide pulse in intact mitochondria in the presence of antimycin, was lost in ubiquinone-depleted membranes, even if cytochromec was added. Readdition of ubiquinone-2 restored the oxidant-induced extrareduction with an apparent half saturation at 1 mol/molbc
1 complex saturating at about 5 mol/mol. These findings demonstrate a requirement for the ubiquinone pool of the cytochromeb extrareduction. Since the initial rates of cytochromeb reoxidation upon ferricyanide addition, in the presence of antimycin, did not saturate by any ferricyanide concentration in ubiquinone-depleted mitochondria, a direct chemical reaction between ferricyanide and reduced cytochromeb was postulated. The fact that such direct reaction is much faster in ubiquinone-depleted mitochondria may explain the lower antimycin sensitivity of the succinate ferricyanide reductase activity after removal of endogenous ubiquinone. 相似文献
8.
Migliore M 《Journal of computational neuroscience》2003,14(2):185-192
Using a realistic model of a CA1 hippocampal pyramidal neuron, we make experimentally testable predictions on the roles of the non-specific cation current, I
h
, and the A-type Potassium current, I
A
, in modulating the temporal window for the integration of the two main excitatory afferent pathways of a CA1 neuron, the Schaffer Collaterals and the Perforant Path. The model shows that the experimentally observed increase in the dendritic density of I
h
and I
A
could have a major role in constraining the temporal integration window for these inputs, in such a way that a somatic action potential (AP) is elicited only when they are activated with a relative latency consistent with the anatomical arrangement of the hippocampal circuitry. 相似文献
9.
Many bacteria adapt to microoxic conditions by synthesizing a particular cytochrome c oxidase (cbb
3) complex with a high affinity for O2, encoded by the ccoNOQP operon. A survey of genome databases indicates that ccoNOQP sequences are widespread in all sub-branches of Proteobacteria but otherwise are found only in bacteria of the CFB group (Cytophaga, Flexibacter, Bacteroides). Our analysis of available genome sequences suggests four major strategies of regulating ccoNOQP expression in response to O2. The most widespread strategy involves direct regulation by the O2-responsive protein Fnr. The second strategy involves an O2-insensitive paralogue of Fnr, FixK, whose expression is regulated by the O2-responding FixLJ two-component system. A third strategy of mixed regulation operates in bacteria carrying both fnr and fixLJ-fixK genes. Another, not yet identified, strategy is likely to operate in the -Proteobacteria Helicobacter pylori and Campylobacter jejuni which lack fnr and fixLJ-fixK genes. The FixLJ strategy appears specific for the -subclass of Proteobacteria but is not restricted to rhizobia in which it was originally discovered. 相似文献
10.
Sialidases cleave off sialic acid residues from the oligosaccharide chain of gangliosides in their catabolic pathway while sialyltransferases transfer sialic acid to the growing oligosaccharide moiety in ganglioside biosynthesis. Ganglioside GM3 is a common substrate for both types of enzymes, for sialidase acting on ganglioside GM3 as well as for ganglioside GD3 synthase. Therefore, it is possible that both enzymes recognize similar structural features of the sialic acid moiety of their common substrate, ganglioside GM3. Based on this idea we used a variety of GM3 derivatives as glycolipid substrates for a bacterial sialidase (Clostridium perfringens) and for GD3 synthase (of rat liver Golgi vesicles). This study revealed that those GM3 derivatives that were poorly degraded by sialidase also were hardly recognized by sialyltransferase (GD3 synthase). This may indicate similarities in the substrate binding sites of these enzymes. 相似文献
11.
David J. Castillo Teresa Ballado Laura Camarena Georges Dreyfus 《Antonie van Leeuwenhoek》2009,95(1):77-90
The single subpolar flagellum of Rhodobacter sphaeroides shows an enlarged hook-filament junction. One of the two proteins that compose this section of the filament is HAP1
Rs
(FlgK
Rs
) it contains a central non-conserved region of 860 amino acids that makes this protein about three times larger than its
homologue in Salmonella enterica serovar Typhimurium. We investigated the role of this central portion of the unusually large HAP1 protein of R. sphaeroides by monitoring the effects of serial deletions in flgK
Rs
, the gene encoding HAP1
Rs
, on swimming and swarming. Two deletion mutants did not assemble functional flagella, two were paralyzed and five exhibited
reduced free-swimming speeds. Some mutants produced unusual swarming patterns on soft agar without or with Ficoll 400. A segment
of approximately 200-aa of the central region of HAP1
Rs
that aligns with the variable region of the flagellin sequence from other γ- and β-proteobacteria was also found. Therefore,
it is possible that the origin of this large central domain of HAP1
Rs
could be associated with an event of horizontal transfer and subsequent duplications and/or insertions. 相似文献
12.
Yan Li Heng Yin Qing Wang Xiaoming Zhao Yuguang Du Fenglan Li 《Carbohydrate polymers》2009,75(4):612-617
NO (nitric oxide) and H2O2 (hydrogen peroxide) are important signaling molecule in plants. Brassica napus L. was used to understand oligochitosan inducing production of NO (nitric oxide) and H2O2 (hydrogen peroxide) and their physiological function. The result showed that the production of NO and H2O2 in epidermal cells of B. napus L. was induced with oligochitosan by fluorescence microscope. And it was proved that there was an interaction between NO and H2O2 with L-NAME (NG-nitro-l-arg-methyl eater), which is an inhibitor of NOS (NO synthase) in mammalian cells that also inhibits plant NO synthesis, and CAT (catalase), which is an important H2O2 scavenger, respectively. It was found that NO and H2O2 induced by oligochitosan took part in inducing reduction in stomatal aperture and LEA protein gene expression of leaves of B. napus L. All these results showed that oligochitosan have potential activities of improving resistance to water stress. 相似文献
13.
Vassalle M 《Journal of biomedical science》2007,14(6):699-716
Summary The mechanisms underlying the pacemaker current in cardiac tissues is not agreed upon. The pacemaker potential in Purkinje
fibers has been attributed to the decay of the potassium current I
Kdd. An alternative proposal is that the hyperpolarization-activated current I
f underlies the pacemaker potential in all cardiac pacemakers. The aim of this review is to retrace the experimental development
related to the pacemaker mechanism in Purkinje fibers with reference to findings about the pacemaker mechanism in the SAN
as warranted. Experimental data and their interpretation are critically reviewed. Major findings were attributed to K+ depletion in narrow extracellular spaces which would result in a time dependent decay of the inward rectifier current I
K1. In turn, this decay would be responsible for a “fake” reversal of the pacemaker current. In order to avoid such a postulated
depletion, Ba2+ was used to block the decay of I
K1. In the presence of Ba2+ the time-dependent current no longer reversed and instead increased with time and more so at potentials as negative as −120 mV.
In this regard, the distinct possibility needs to be considered that Ba2+ had blocked I
Kdd (and not only I
K1). That indeed this was the case was demonstrated by studying single Purkinje cells in the absence and in the presence of
Ba2+. In the absence of Ba2+, I
Kdd was present in the pacemaker potential range and reversed at E
K. In the presence of Ba2+, I
Kdd was blocked and I
f appeared at potentials negative to the pacemaker range. The pacemaker potential behaves in a manner consistent with the underlying
I
Kdd but not with I
f. The fact that I
f is activated on hyperpolarization at potential negative to the pacemaker range makes it suitable as a safety factor to prevent
the inhibitory action of more negative potentials on pacemaker discharge. It is concluded that the large body of evidence
reviewed proves the pacemaker role of I
Kdd (but not of I
f) in Purkinje fibers. 相似文献
14.
Joseph E. Neigel 《Conservation Genetics》2002,3(2):167-173
Since the introduction of allozyme methods inthe mid 1960s it has been a standard practiceto report Wright's measure of populationsubdivision, F
ST, for surveys ofgenetic variation. Its widespread use hasprovided us with a sense of what values can beexpected in particular situations and how theycan be interpreted. With some theoreticaljustification, F
ST has also beenused to estimate rates of gene flow. Howeverthere are conditions under which F
STis inappropriate for gene flow estimation andcan lead to incorrect or even absurdconclusions. These pitfalls have promptedcritics to suggest that F
ST hasfailed to deliver what its proponents havepromised and should be abandoned. A furtherchallenge has been the development of newmethods that offer even greater promise. Thusit is reasonable to ask if perhaps it is timeto retire F
ST and turn to new andmore powerful methods for the inference of geneflow from genetic markers. Here I will arguethat although gene flow should be estimated bymore powerful approaches whenever practical,F
ST remains a useful measure of theaverage effects of gene flow and will continueto be used for comparative purposes. 相似文献
15.
Cai J Zeng H Shima Y Hatabayashi H Nakagawa H Ito Y Adachi Y Nakajima H Yabe K 《Fungal genetics and biology : FG & B》2008,45(7):1081-1093
The nadA gene is present at the end of the aflatoxin gene cluster in the genome of Aspergillus parasiticus as well as in Aspergillus flavus. RT-PCR analyses showed that the nadA gene was expressed in an aflatoxin-inducible YES medium, but not in an aflatoxin-non-inducible YEP medium. The nadA gene was not expressed in the aflR gene-deletion mutant, irrespective of the culture medium used. To clarify the nadA gene’s function, we disrupted the gene in aflatoxigenic A. parasiticus. The four nadA-deletion mutants that were isolated commonly accumulated a novel yellow-fluorescent pigment (named NADA) in mycelia as well as in culture medium. When the mutants and the wild-type strain were cultured for 3 days in YES medium, the mutants each produced about 50% of the amounts of G-group aflatoxins that the wild-type strain produced. In contrast, the amounts of B-group aflatoxins did not significantly differ between the mutants and the wild-type strain. The NADA pigment was so unstable that it could non-enzymatically change to aflatoxin G1 (AFG1). LC–MS measurement showed that the molecular mass of NADA was 360, which is 32 higher than that of AFG1. We previously reported that at least one cytosol enzyme, together with two other microsome enzymes, is necessary for the formation of AFG1 from O-methylsterigmatocystin (OMST) in the cell-free system of A. parasiticus. The present study confirmed that the cytosol fraction of the wild-type A. parasiticus strain significantly enhanced the AFG1 formation from OMST, whereas the cytosol fraction of the nadA-deletion mutant did not show the same activity. Furthermore, the cytosol fraction of the wild-type strain showed the enzyme activity catalyzing the reaction from NADA to AFG1, which required NADPH or NADH, indicating that NADA is a precursor of AFG1; in contrast, the cytosol fraction of the nadA-deletion mutant did not show the same enzyme activity. These results demonstrated that the NadA protein is the cytosol enzyme required for G-aflatoxin biosynthesis from OMST, and that it catalyzes the reaction from NADA to AFG1, the last step in G-aflatoxin biosynthesis. 相似文献
16.
I. Batlle F. H. Alston 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1996,93(1-2):179-182
Mildew resistance in the ornamental apple White Angel was found to be determined by complementary genes. The gene R
w
was found to be necessary for the expression of resistance controlled by the resistance gene Pl
w
. The close linkage between the isoenzyme gene, Lap-2, for leucine aminopeptidase and P1
w
was confirmed. The efficiency of Lap-2 as a marker in screening for mildew resistance is limited, as it cannot account for susceptible plants with the r
w
r
w
P1
w
p1
w
genotype. It has, however, an important role to play in combining resistance genes from different sources. The genotypes of White Angel (R
w
r
w
, Pl
w
pl
w
, Lap-2an), Jester (R
w
r
w
, p1
w
p
w
, Lap-2an) Katja (R
w
r
w
,p1
w
p1
w
, Lap-2an) and Gloster 69 (r
w
r
w
, p1
w
p1
w
, Lap-2an) were determined. It also appeared that R
w
might influence Lap-2 activity in young seedlings. 相似文献
17.
为探讨氮沉降对九寨沟藓类植物的影响,该研究以当地优势藓类植物锦丝藓(Actinothuidium hookeri)和塔藓(Hylocomium splendens)为对象,以NH4NO3为氮源,设置对照(0 kg N·hm-2·a-1)、低浓度(20 kg N·hm-2·a-1)、高浓度(50 kg N·hm-2·a-1)3种处理,开展为期6个月的氮沉降模拟实验。结果表明:(1)氮沉降处理导致两种藓类植物的活性氧、丙二醛、叶绿素、脯氨酸和可溶性蛋白含量显著增加,同时锦丝藓过氧化氢酶、过氧化物酶、超氧化物歧化酶、抗坏血酸过氧化物酶活性增加。(2)对于生长旺期和生长末期的塔藓,氮沉降导致其过氧化物酶、过氧化氢酶、抗坏血酸过氧化物酶活性降低。(3)锦丝藓的综合隶属函数值随氮沉降浓度增大而增加,在生长旺期和生长末期,塔藓综合隶属函数值对氮沉降的响应存在差异。综上认为,两种藓类植物对氮沉降处理的生理响应存在差异,高浓度氮沉... 相似文献
18.
Liu H.Q. Jiang G.M. Zhang Q.D. Sun J.Z. Guo R.J. Gao L.M. Bai K.Z. Kuang T.Y. 《Photosynthetica》2002,40(2):237-242
Three winter wheat (Triticum aestivum L.) cultivars, representatives of those widely cultivated in Beijing over the past six decades, were grown in the same environmental conditions. Net photosynthetic rate (P
N) per unit leaf area and instantaneous water use efficiency (WUE) of flag leaves increased with elevated CO2 concentration. With an increase in CO2 concentration from 360 to 720 µmol mol–1, P
N and WUE of Jingdong 8 (released in 1990s and having the highest yield) increased by 173 and 81 %, while those of Nongda 139 (released in 1970s) increased by 88 and 66 %, and Yanda 1817 (released in 1945, with lowest yield) by 76 and 65 %. Jingdong 8 had the highest P
N and WUE values under high CO2 concentration, but Yanda 1817 showed the lowest P
N. Stomatal conductance (g
s) of Nongda 139 and Yanda 1817 declined with increasing CO2 concentration, but g
s of Jingdong 8 firstly went down and then up as the CO2 concentration further increased. Intercellular CO2 concentration (C
i) of Jingdong 8 and Nongda 139 increased when CO2 concentration elevated, while that of Yanda 139 increased at the first stage and then declined. Jingdong 8 had the lowest C
i of the three wheat cultivars, and Yanda 1817 had the highest C
i value under lower CO2 concentrations. However, Jingdong 8 had the highest P
N and lowest C
i at the highest CO2 concentration which indicates that its photosynthetic potential may be high. 相似文献
19.
Bernad S Leygue N Korri-Youssoufi H Lecomte S 《European biophysics journal : EBJ》2007,36(8):1039-1048
Cytochrome c
552 (Cyt-c
552) and its redox partner ba
3
-oxidase from Thermus thermophilus possess structural differences compared with Horse heart cytochrome c (cyt-c)/cytochrome c oxidase (CcO) system, where the recognition between partners and the electron transfer (ET) process is initiated via electrostatic
interactions. We demonstrated in a previous study by surface-enhanced resonance Raman (SERR) spectroscopy that roughened silver
electrodes coated with uncharged mixed self-assembled monolayers HS–(CH2)
n
–CH3/HS–(CH2)
n + 1–OH 50/50, n = 5, 10 or 15, was a good model to mimic the Cyt-c
552 redox partner. All the adsorbed molecules are well oriented on such biomimetic electrodes and transfer one electron during
the redox process. The present work focuses on the kinetic part of the heterogeneous ET process of Cyt-c
552 adsorbed onto electrodes coated with such mixed SAMs of different alkyl chain length. For that purpose, two complementary
methods were combined. Firstly cyclic voltammetry shows that the ET between the adsorbed Cyt-c
552 and the biomimetic electrode is direct and reversible. Furthermore, it allows the estimation of both the density surface
coverage of adsorbed Cyt-c
552 and the kinetic constants values. Secondly, time-resolved SERR (TR-SERR) spectroscopy showed that the ET process occurs without
conformational change of the Cyt-c
552 heme group and allows the determination of kinetic constants. Results show that the kinetic constant values obtained by TR-SERR
spectroscopy could be compared to those obtained from cyclic voltammetry. They are estimated at 200, 150 and 40 s−1 for the ET of Cyt-c
552 adsorbed onto electrodes coated with mixed SAMs HS–(CH2)
n
–CH3/HS–(CH2)
n + 1–OH 50/50, n = 5, 10 or 15, respectively.
Presented at the joint biannual meeting of the SFB-GEIMM-GRIP, Anglet France, 14–19 October, 2006. 相似文献
20.
Desjardins AE Li YX Reinker S Miura RM Neuman RS 《Journal of computational neuroscience》2003,15(2):131-142
Recent experimental and theoretical studies have found that active dendritic ionic currents can compensate for the effects of electrotonic attenuation. In particular, temporal summation, the percentage increase in peak somatic voltage responses invoked by a synaptic input train, is independent of location of the synaptic input in hippocampal CA1 pyramidal neurons under normal conditions. This independence, known as normalization of temporal summation, is destroyed when the hyperpolarization-activated current, I
h, is blocked [Magee JC (1999a), Nature Neurosci. 2: 508–514]. Using a compartmental model derived from morphological recordings of hippocampal CA1 pyramidal neurons, we examined the hypothesis that I
h was primarily responsible for normalization of temporal summation. We concluded that this hypothesis was incomplete. With a model that included I
h, the persistent Na+ current (I
NaP), and the transient A-type K+ current (I
A), however, we observed normalization of temporal summation across a wide range of synaptic input frequencies, in keeping with experimental observations. 相似文献