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91.
Invasion of tissue culture cells by diarrhoeagenic strains of Escherichia coli which lack the enteroinvasive inv gene 总被引:2,自引:0,他引:2
Aberra Geyid Jon Fletcher Brehanu A. Gashe Åsa Ljungh 《FEMS immunology and medical microbiology》1996,14(1):15-24
Abstract Invasive Escherichia coli strains of certain serotypes invade by the same mechanism as the Shigella sp. It has been proposed that invasion of epithelial cells by EPEC strains may also occur; this is a previously overlooked property. In the present study E. coli strains isolated from patients with diarrhoea or ulcerative colitis, lacking the inv plasmid mediating classical invasion, but hybridizing with probes for different adhesins, were analyzed for their ability to invade HeLa and Caco-2 cells. The majority of strains invaded Caco-2 cells to a higher extent than HeLa cells. Adhesion to Caco-2 cells was a prerequisite for subsequent invasion of the cells but EAF, eae , EAgg and other known virulence factors were not sufficient to mediate invasion. In 8/9 E. coli strains invasion was enhanced after growth under iron restriction. Growth during anaerobic conditions did not influence subsequent invasion by E. coli strains whereas 6/9 strains had their invasive ability significantly decreased after growth in the presence of 1% glucose. The invasive process was inhibited by mannose but not by lactose, fucose or galactose. Our data indicate that strains of E. coli may invade Caco-2 cells by novel mechanisms which require adhesion to the cells but which differ from those of Salmonella sp., Yersinia sp., Shigella sp. and classical enteroinvasive E. coli . 相似文献
92.
Ricardo O. Louro Teresa Catarino Carlos A. Salgueiro Jean LeGall António V. Xavier 《Journal of biological inorganic chemistry》1996,1(1):34-38
Using potentiometric titrations, two protons were found to participate in the redox-Bohr effect observed for cytochrome c
3 from Desulfovibrio vulgaris (Hildenborough). Within the framework of the thermodynamic model previously presented, this finding supports the occurrence
of a concerted proton-assisted 2e– step, ideally suited for the coupling role of cytochrome c
3 to hydrogenase. Furthermore, at physiological pH, it is shown that when sulfate-reducing bacteria use H2 as energy source, cytochrome c
3 can be used as a charge separation device, achieving energy transduction by energising protons which can be left in the acidic
periplasmic side and transferring deenergised electrons to sulfate respiration. This mechanism for energy transduction, using
a full thermodynamic data set, is compared to that put forward to explain the proton-pumping function of cytochrome c oxidase. 相似文献
93.
利用离休孵育脑薄片和放射免疫测定其释放的精氨酸加压素(AVP)方法,探讨糖皮质激素(GC)在不能进入细胞内的情况下,对去肾上腺大鼠的下丘脑薄片释放AVP的快速影响及其可能的细胞膜机制。结果如下:(1)下丘脑薄片能够稳定地释放AVP(2h),其释放量为15.42±1.28pg/min;(2)牛血清白蛋白耦联皮质酮(B-BSA)对AVP的释放具有快速的(20min)抑制性效应,在10 ̄(-7)─10 ̄(-4)mol/L范围内呈剂量一效应关系;(3)GC细胞内受体拮抗剂RU486(10 ̄(-4)─10 ̄(-3)mol/L)能部分地阻断B─BSA的快速抑制效应;(4)孵育液中Ca ̄(2+)程度升高,B─BSA的快速抑制效应明显增强;反之,孵育液中无Ca ̄(2+)则B-BSA的快速抑制效应有所减弱。表明GC在未进入细胞内的情况下也可快速地抑制大鼠下丘脑薄片释放AVP,因此没有通过传统的基因组机制,而是由非基因组机制介导的,其作用部位在细胞膜水平上,可能是影响Ca ̄(2+)的跨细胞膜内流通量或/和影响有Ca ̄(2+)参与的AVP释放过程的结果。 相似文献
94.
丝氨酸蛋白酶抑制剂的研究及应用 总被引:4,自引:0,他引:4
丝氨酸蛋白酶抑制剂(serpin)是一类结构、序列同源的蛋白酶抑制剂,它是体内许多蛋白水解级联反应的调节因子,其遗传性结构或分泌异常将导致许多疾病.因此对于其结构及作用机理的研究将为临床应用提供依据. 相似文献
95.
超低能重离子注入作物育种的原初物理机制 总被引:2,自引:0,他引:2
从原子核物理学观点出发,采用理论分析与实验测量并举的方法对超级能(〈200kev)重离子(Z≥6)注入作物(小麦)种子进行诱变育种的原初物理机制进行了研究,结果表明,无论是注入离子本身的射程,还是次级电子,自由基扩散,高温热穗,级联原子和冲击波等次级作用范围都无法触及表皮下面的胚细胞,但注入离子在麦胚内主要元素(C,N,O,S,P,K,Ca)上激发出的特征X-射线,在其强度减弱为原来的10^-3时 相似文献
96.
Thomas Hiltonen Jan Karlsson Kristin Palmqvist Adrian K. Clarke Göran Samuelsson 《Planta》1995,195(3):345-351
An intracellular carbonic anhydrase (CA; EC 4.2.1.1) was purified and characterised from the unicellular green alga Coccomyxa sp. Initial studies showed that cultured Coccomyxa cells contain an intracellular CA activity around 100 times higher than that measured in high-CO2-grown cells of Chlamydomonas reinhardtii CW 92. Purification of a protein extract containing the CA activity was carried out using ammonium-sulphate precipitation followed by anion-exchange chromatography. Proteins were then separated by native (non-dissociating) polyacrylamide gel electrophoresis, with each individual protein band excised and assayed for CA activity. Measurements revealed CA activity associated with two discrete protein bands with similar molecular masses of 80 +5 kDa. Dissociation by denaturing polyacrylamide gel electrophoresis showed that both proteins contained a single polypeptide of 26 kDa, suggesting that each 80-kDa native protein was a homogeneous trimer. Isoelectric focusing of the 80-kDa proteins also produced a single protein band at a pH of 6.5. Inhibition studies on the purified CA extract showed that 50% inhibition of CA activity was obtained using 1 M azetazolamide. Polyclonal antibodies against the 26-kDa CA were produced and shown to have a high specific binding to a single polypeptide in soluble protein extracts from Coccomyxa cells. The same antiserum, however, failed to cross-react with soluble proteins isolated from two different species of green algae, Chlamydomonas reinhardtii and Chlorella vulgaris. Correspondingly, antisera directed against pea chloroplastic CA, extracellular CA from C. reinhardtii and human CAII, showed no cross-hybridisation to the 26-kDa polypeptide in Coccomyxa. The 26-kDa protein was confirmed as being a CA by N-terminal sequencing of two internal polypeptide fragments and alignment of these sequences with that of previously identified CA proteins from several different species.Abbreviations CA
carbonic anhydrase
- CCM
CO2-concentrating mechanism
- IEF
isoelectric focusing
- Rubisco
ribulose-l,5-bisphosphate carboxylase/oxygenase
We would like to thank Drs. Cecilia Forsman, Inga-Maj Johansson and Nalle Jonsson for their valuable advice concerning the isolation of CA. This work was supported by the Swedish Natural Research Council and Seth M. Kempes Memorial foundation. 相似文献
97.
Net O2 evolution, gross CO2 uptake and net HCO
inf3
su–
uptake during steady-state photosynthesis were investigated by a recently developed mass-spectrometric technique for disequilibrium flux analysis with cells of the marine cyanobacterium Synechococcus PCC7002 grown at different CO2 concentrations. Regardless of the CO2 concentration during growth, all cells had the capacity to transport both CO2 and HCO
inf3
su–
; however, the activity of HCO
inf3
su–
transport was more than twofold higher than CO2 transport even in cyanobacteria grown at high concentration of inorganic carbon (Ci = CO2 + HCO
inf3
su–
). In low-Ci cells, the affinities of CO2 and HCO
inf3
su–
transport for their substrates were about 5 (CO2 uptake) and 10 (HCO
inf3
su–
uptake) times higher than in high-Ci cells, while air-grown cells formed an intermediate state. For the same cells, the intracellular accumulated Ci pool reached 18, 32 and 55 mM in high-Ci, air-grown and low-Ci cells, respectively, when measured at 1 mM external Ci. Photosynthetic O2 evolution, maximal CO2 and HCO
inf3
su–
transport activities, and consequently their relative contribution to photosynthesis, were largely unaffected by the CO2 provided during growth. When the cells were adapted to freshwater medium, results similar to those for artificial seawater were obtained for all CO2 concentrations. Transport studies with high-Ci cells revealed that CO2 and HCO
inf3
su–
uptake were equally inhibited when CO2 fixation was reduced by the addition of glycolaldehyde. In contrast, in low-Ci cells steady-state CO2 transport was preferably reduced by the same inhibitor. The inhibitor of carbonic anhydrase ethoxyzolamide inhibited both CO2 and HCO
inf3
su–
uptake as well as O2 evolution in both cell types. In high-Ci cells, the degree of inhibition was similar for HCO
inf3
su–
transport and O2 evolution with 50% inhibition occurring at around 1 mM ethoxyzolamide. However, the uptake of CO2 was much more sensitive to the inhibitor than HCO
inf3
su–
transport, with an apparent I50 value of around 250 M ethoxyzolamide for CO2 uptake. The implications of our results are discussed with respect to Ci utilisation in the marine Synechococcus strain.Abbreviations Chl
chlorophyll
- Ci
inorganic carbon (CO2 + HCO
inf3
su–
)
- CA
carbonic anhydrase
- CCM
CO2-concentrating mechanism
- EZA
ethoxyzolamide
- GA
glycolaldehyde
- K1/2
concentration required for half-maximal response
- Rubisco
ribulose-1,5,-bisphosphate carboxylase-oxygenase
D.S. is a recipient of a research fellowship from the Deutsche Forschungsgemeinschaft (D.F.G.). In addition, we are grateful to Donald A. Bryant, Department of Molecular and Cell Biology and Center of Biomolecular Structure Function, Pennsylvania State University, USA, for sending us the wild-type strain of Synechococcus PCC7002. 相似文献
98.
The knopper gallwasp Andricus quercuscalicis Burgsdorf 1783 (Hymenoptera: Cynipidae) has invaded western and northern Europe from southern and eastern Europe over the last 400 years. A. quercuscalicis has two alternating generations, which differ in phenology, structure, and host oak species. This study describes geographic variation in the community in the tiny catkin galls of the sexual generation on Turkey oak, Quercus cerris, and compares the patterns obtained with those in the community attacking the alternate agamic generation. As predicted from considerations of parasitoid recruitment to the communities of invading phytophagous insects (Cornell and Hawkins 1993), in its native range the sexual generation shows (1) higher parasitoid community species richness, (2) higher total mortality due to parasitoid attack and (3) a higher ratio of specialist to generalist parasitoid species than is evident in the invaded range. Counter to predictions, there is no indication that parasitoid community richness in the invaded range has increased with time since the arrival of the new host. Higher host mortality in the native range is due principally to a single specialist, Aulogymnus obscuripes Mayr 1877 (Hymenoptera: Eulophidae), and is not distributed evenly among parasitoid species which attack the gall-former only in this area. This contrasts with the community in Britain, where three principal generalist parasitoids cause approximately equal mortalities. The agamic gall contains a taxonomically and structurally diverse guild of parasitoid and inquiline species, associated with the changing resource provided by a large, long-lived, complex gall. In contrast, the sexual community includes a taxonomically and structurally narrow guild, associated with a resource which is structurally simple, small in size and short-lived. No parasitoid species attacks the gall-former in both generations. Surprisingly, in spite of these differences in the nature of the gall resource in the two generations, over their entire range (native and invaded) the parasitoid guilds of the two are equally species rich. 相似文献
99.
The rate of Hg2+-assisted chloride release from several mer-[CrCl(diamine)(triamine)]2+ complexes has been measured as a function of pressure, Hg2+ concentration and temperature. The calculated activation volumes are independent of [Hg2+] and temperature and kinetic parametes 104 kHg (25 °c) (M−1 s−1), ΔH‡ (kJ mol−1), ΔS‡ (J K−1 mol−1), ΔV‡ (cc mol−1) are: (en)(dpt): 6.44. 75.5, −52, −5.0; (ibn)(dpt): 5.81, 89.5, −6, −0.03; (Me2tn)(dpt): 22.2, 84.9, −11, −0.5; (tn)(dpt): 29.1, 87, −1, +0.3; (en)(2,3-tri): 1.94, 87.0, −24, −5.7; (en)(Medpt): 0.417, 94.6, −11, −0.8; (tn)(Medpt): 9.14, 98.3, +26, +1.8. 相似文献
100.
Raffaello Romeo Giuseppe Arena Luigi Mons Scolaro Maria Rosario Plutino 《Inorganica chimica acta》1995,240(1-2):81-92
The rates of displacement of dimethyl sulfoxide from the cation [Pt(phen) (CH3) (Me2SO)]+ by a series of uncharged and negatively charged nucleophiles have been measured in a methanol/water (19:1 vol./vol.) mixture. The starting complex and the reaction products were characterized either as solids or in solution by their IR and 1H NMR spectra. The substitution reactions take place by way of a direct bimolecular attack of the ligand on the substrate. The sequence of reactivity observed is as expected on the basis of a nucleophilicity scale relevant for + 1 charged substrates ([Pt(en) (NH3)Cl]+ used as standard). The difference of reactivity between the first (t-BuNH2) and the last (SeCN−) members of the series spans five orders of magnitude. The value measured for the nucleophilic discrimination (1.55) is the highest found so far for cationic substrates. This is a result of the easy transfer of some of the electron density brought in by the incoming ligand into the ancillary ligands. When the reaction is carried out in a series of protic and dipolar aprotic solvents, using chloride ion as nucleophile, the rate of formation of [Pt (phen) (CH3)Cl] is dominated by the extent of solvation of Cl−, as measured by its values of the Gibbs molar energy of transfer ΔtG0. Conductivity measurements at 25°C in dichloromethane were fitted to the Fuoss equation and the values of the dissociation constants Kd for the ion pairs were calculated as follows: 2.27 × 10−5 M for Bu4NCl, 2.75 × 10−5 M for Bu4NSCN and 17.05 × 10−5 M for [Pt(phen) (CH3) (Me2SO)]PF6. The pseudo-first-order rate constants kobs for the reactions with Bu4NCl, Bu4NBr, Bu4NSCN and Bu4NI showed a curvilinear dependence on the concentration of the salt which levels off very soon (at concentrations higher than 0.005 M the kinetics are zero order in [Bu4NX]). On addition of the inert electrolyte Bu4NPF6 the rates slow down and the kinetics follow the rate law kobs = kKip[Bu4NX]/[Bu4NPF6] + Kip[Bu4NX]). These findings fit well with a reaction scheme which involves a pre-equilibrium Kip between ion pairs, followed by unimolecular substitution within the contact ion pair [Pt(phen) (CH3) (Me2SO)X]ip. Values of the equilibrium constants Kip for ion-pair exchange and of the internal substitution rates k were derived. The latter showed that the discrimination in reactivity between Cl−, Br−, SCN− and I− is greatly reduced with respect to aqueous solutions. The reason behind this may be desolvation of the ions coupled to the fact that a contact ion pair is already at a certain distance along the reaction coordinate in the direction of the transition state. Applications of the special salt effect and of ion pairing to synthesis are discussed. 相似文献