| 1. |
- Björck, Lars, et al.
(författare)
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Bacterial growth inhibited by a synthetic inhibitor based upon the structure of a human proteinase inhibitor
- 1989
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 337:6205, s. 385-386
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Tidskriftsartikel (refereegranskat)abstract
- Cysteine proteinases are important not only in the intracellular catabolism of peptides and proteins1 and in the processing of prohormones and proenzymes2,3, but also in the penetration of normal human tissue by malignant cells4 and possibly microorganisms5, including viruses. Cystatin C is a human cysteine proteinase inhibitor present in extracellular fluids6. We have synthesized peptide derivatives mimicking the proposed proteinase-binding centre of cystatin C7 and find that they irreversibly inhibit cysteine proteinases. Several bacteria produce proteinases, so we tested a tripeptide derivative (Z-LVG-CHN2) for in vitro anti-bacterial activity against a large number of bacterial strains belonging to thirteen different species. It was found to inhibit specifically the growth of all strains of group A streptococci. The susceptibility of these human pathogens to the peptide was compared with that to well-established anti-streptococcal antibiotics such as tetracy-cline and bacitracin. Moreover, the peptide was active in vivo against group A streptococci: mice injected with lethal doses of these bacteria were cured by a single injection of Z-LVG-CHN2. The cysteine proteinase produced by group A streptococci was isolated and found to be inhibited by Z-LVG-CHN2; moreover, excess proteinase relieved the growth inhibition caused by the peptide derivative, suggesting that the antibacterial activity of Z-LVG-CHN2 is due to inhibition of this cysteine proteinase. This strategy of blocking proteinases with peptide derivatives that mimic naturally occurring inhibitors could be useful in the construction of new agents against other microorganisms, including viruses.
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| 2. |
- Bovin, JO, et al.
(författare)
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Imaging of atomic clouds outside the surfaces of gold crystals by electron microscopy
- 1985
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 317, s. 47-49
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Tidskriftsartikel (refereegranskat)abstract
- The structure of small metal crystals has been intensively examined by high-resolution electron microscopy (HREM). In particular, multiply-twinned gold and silver crystals have been characterized using the profile-imaging method1,2 at atomic resolution, and reconstructed metal surfaces observed2. Crystal structure images of large gold clusters consisting of 55 gold atoms arranged in a cubeoctahedron have been recorded3 using 2.5 Å resolution, and crystal growth, row by row, on a {111} surface has been documented4 using a low-light-level silicon-intensified target television (TV) camera and video system with an on-line image processor. Direct imaging of rearrangements of atomic columns on extended gold surface5 established that profile imaging can provide information about surface self-diffusion. The motion of surface atoms, recorded with a real-time video tape-recorder (VTR) system, and the formation of surface atom steps on {100} surfaces, although not {111}, has also been reported recently6. Dynamic HREM observations at TV rate showing defect motion in gold7 and CdTe (refs. 8, 9) has given information on ‘in-lattice’ rearrangements of columns of atoms. We report here surface profile images recorded with the electron beam along the 〈110〉 direction with spatial resolution of ∼2.0 Å which reveal changes in occupancy of the atom columns often within periods of less than 0.1 s. Surfaces with several adjacent atom columns involved in rapid structural changes frequently interacted with a cloud of atoms extending out to 9 Å off the crystal and changes in shape and density of the clouds were recorded. Although these clouds have already been described6,10, the present work is the first to analyse these events properly and to describe them in detail. The motion of atomic columns and the existence of atom clouds revealed here may have important consequences for crystal growth, surface science and catalysis studies.
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| 3. |
- Coron, N., et al.
(författare)
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A Composite Bolometer as a Charged-Particle Spectrometer
- 1985
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 314:6006, s. 75-76
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Tidskriftsartikel (refereegranskat)abstract
- The measurement of radioactivity by direct conversion of nuclear radiation into a temperature rise of a calorimeter is as old as nuclear physics itself. As part of a general programme aiming at a determination of the mass of the electron neutrino, we have designed an improved version of a He-cooled composite diamond bolometer with a monolithic germanium thermistor, developed at the Laboratoire de Physique Stellaire et Planetaire (LPSP)1. Our approach, based on an idea by De Rujula2, is to study the shape, near the upper end-point of the internal bremsstrahlung spectrum in electron-capture β decay. The best nucleus for a precise measurement seems to be 163Ho, for which we have determined3 the Q EC value to be 2.83±0.05 keV. A particularly interesting possibility is to use total absorption spectrometry4 (calorimetry), in which the radioactive holmium forms part of the sensitive volume of the detector. With 5–6-MeV α particles impinging on the diamond wafer of the bolometer, a full-width-at-half-maximum (FWHM) of 36 keV was obtained at a temperature of 1.3 K. The theoretical resolution at 100 mK is a few electron-volts, so this new detection technique should give greatly enhanced energy resolution compared with present solid-state conductors based on charge carrier collection.
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| 4. |
- Hansen, Staffan, et al.
(författare)
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Oxidation Catalysis on YBa2Cu3O6 + x
- 1988
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 334:6178, s. 143-145
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Tidskriftsartikel (refereegranskat)abstract
- Mild oxidation catalysts are used to product a wide range industrial chemicals from hydrocarbons, whereas deep oxidation catalysts yield CO2 and are becoming important in the cleaning of emissions from combustion of carbonaceous fuels. Here we report on a catalyst1 that facilitates both mild and deep oxidation of toluene in the presence of molecular oxygen and ammonia. At low partial pressures of O2a YBa2Cu3O6+x catalyst is very active in the formation of benzonitrile, but at higher O2 partial pressures it preferentially catalyses formation of CO2. This sharp transition in product selectivity is reversible and occurs at a defined partial pressure of O2. At transition the bulk compostition of the catalyst is close to YBa2Cu3O6 (x≈0). Increasing the content of lattice oxygen (x > 0) makes the catalyst selective for CO2 formation
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| 5. |
- Larsson, Per
(författare)
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Contaminated sediments of lakes and oceans act as sources of chlorinated hydrocarbons for release to water and atmosphere
- 1985
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 317, s. 347-349
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Tidskriftsartikel (refereegranskat)abstract
- Atmospheric transport is a major route for entry of chlorinated, aromatic hydrocarbons into aquatic ecosystems. Once in the water, the compounds are readily taken up by the biota and distributed in the food webs. Major fractions of the compounds are deposited in the sediment1, and it had been thought that most persistent contaminants are inactivated in this way as a consequence of their lipophilic properties. However, results from recent laboratory studies2,3 raise the possibility that aquatic sediments may not be the final sink for the substances but may rather act as a source through redistribution of the compounds to water and the atmosphere. Polychlorinated biphenyls (PCBs) may be regarded as 'tracers' for these contaminants in the ecosystem, and I studied the transport of PCBs from sediment to water and air in two artificial ponds in the field. The transport from the sediment followed a seasonal cycle; higher concentrations of PCBs in water and air were recorded in the summer and lower in the winter. PCB concentrations in the air over the ponds were positively correlated with PCB levels in the water. My results show that contaminated sediments may act as a source of chlorinated hydrocarbons released into the environment.
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| 6. |
- Löfstedt, Christer, et al.
(författare)
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Evolution of the ermine moth pheromone tetradecyl acetate
- 1986
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 323:6089, s. 621-623
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Tidskriftsartikel (refereegranskat)abstract
- The nine sympatric forms of small ermine moths of the genus Yponomeuta (Lepidoptere; Yponomeutidae) in the west palaearctic region show various degrees of differentiation1,2, including among other characteristics, differences in their sexual pheromones3. As is the case for many other moths4, the ermine moths so far analysed use delta 11-unsaturated acetates ((Z)-11-tetradecenyl, (E)-11-tetradecenyl and (Z)-11-hexadecenyl acetate) as primary pheromone components. Here for the first time in Lepidoptera we report that a saturated acetate, tetradecyl acetate, is the primary pheromone component5 of Y. rorellus (Hübner). Y. rorellus is almost monomorphic with respect to isoenzyme variation6 and has fewer chromosomes than its relatives7,8. We suggest that it has evolved through loss of unsaturated pheromone components in a 'genetic revolution' at a population bottleneck, and by the founders of the new species filling an empty communication niche, separated from that of the ancestral species.
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| 7. |
- Moore, R.L., et al.
(författare)
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Superluminal Acceleration in 3C345
- 1983
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Ingår i: Nature. - London, United Kingdom : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 306:5938, s. 44-46
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Tidskriftsartikel (refereegranskat)abstract
- The superluminal quasar 3C345 has a curved, one-sided jet-like radio structure1,2. Ejected material has been observed travelling at apparent speeds of 13–17c (ref. 3). We report here new observations at 22 GHz which show that the most recently ejected component4 is not moving radially away from the compact radio core, but along a trajectory which could be interpreted as either a curved path originating in the compact core, or a straight line, in which case the origin of ejection is not coincident with the compact radio core. The observations provide evidence of acceleration of this component. © 1983 Nature Publishing Group.
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| 8. |
- Olsén, Arne, et al.
(författare)
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Fibronectin binding mediated by a novel class of surface organelles on Escherichia coli
- 1989
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 338:6217, s. 652-5
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Tidskriftsartikel (refereegranskat)abstract
- Gram-negative bacteria are known to produce two types of surface organelles: flagella, which are required for motility and chemotaxis, and pili (fimbriae), which play a part in the interaction of bacteria with other bacteria and with eukaryotic host cells. Here we report a third class of E. coli surface organelles for which we propose the name curli. Curli are coiled surface structures composed of a single type of subunit, the curlin, which differs from all known pilin proteins and is synthesized in the absence of a cleavable signal peptide. Although the gene encoding this structural subunit, crl, is present and transcribed in most natural isolates of E. coli, only certain strains are able to assemble the subunit protein into curli. This assembly process occurs preferentially at growth temperatures below 37 degrees C. The ability of curli to mediate binding to fibronectin may be a virulence-associated property for wound colonization and for the colonization of fibronectin-coated surfaces.
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| 9. |
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| 10. |
- Ross, Russell G., et al.
(författare)
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Unusual PT dependence of thermal conductivity for a clathrate hydrate
- 1981
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Ingår i: Nature. - : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 290:5804, s. 322-323
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Tidskriftsartikel (refereegranskat)abstract
- Molecular clathrate solids1 are crystals with peculiar and interesting properties. Their characteristic feature2 is that one chemical species, the ‘host’, forms a strongly bonded structure, which encages individual molecules of a second ‘guest’ species. There is virtually no chemical bonding between host and guest molecules. The guests are, nevertheless, firmly constrained by high energy barriers. X-ray and neutron diffraction experiments have shown that clathrates have a periodic structure typical of crystalline solids. A clathrate hydrate2 is a host substance consisting of H2O molecules which form an ice-like, hydrogen-bonded structure. Huge geological deposits of clathrate hydrates containing natural gas are known to exist2,3—these deposits may be exploitable, and in searching for clathrate hydrates knowledge of the thermal conductivity, λ, will be important. We present here a preliminary account of the first measurements of λ versus pressure (P) and temperature (T) for a clathrate hydrate. We studied a clathrate hydrate encaging molecules of tetrahydrofuran. Thermal conductivity was measured using the transient hot-wire method4. The accuracy of the measurements was 3% and the precision 1%. The temperature dependence was found to be unusual in that λ(T) has a positive slope (Fig. 1), a feature never before observed with crystalline organic materials. Furthermore, when λ was measured versus P, it was found unexpectedly that λ (P) was constant—behaviour never before reported for a non-metallic material.
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