Antimetabolite-induced increases in the invasive capacity of murine leukaemia L1210 cells

Pretreatment of murine leukaemia L1210 cells with non-lethal concentrations of various antimetabolites increased the in vitro invasive capacity of these cells into monolayers of rat embryo fibroblasts. The increase in invasive capacity was partly correlated with the induced cell cycle arrest. The concomitant increase in cell surface fucosylation and inhibition of invasion with sulphate indicate a role for glycoproteins in this process. Our results suggest that treatment with antimetabolites may lead to a more aggressive phenotype by altering cell surface properties.     

Photoplastic effects in Cd0.2Hg0.8Te

We irradiated Cd_0.2Hg_0.8Te samples at room temperature in the plastic range, with a CO₂ laser beam the wavelength of which (=10 500 nm) is 20% longer than the absorption threshold. We observed a positive photoplastic effect (PPE) of the order _PPE/4 to 5%.     

Oxidative dimerisation of propene to 1,5-hexadiene on Bi-Zn-O catalysts

The oxidative dimerisation of propene to 1,5-hexadiene has been investigated on Bi-Zn-O catalysts. The Bi₄₈ZnO₇₃ phase, observed in the catalysts calcined at 700 ° C is an active and selective catalyst for the formation of 1,5-hexadiene. The best catalytic performance (1,5-hexadiene selectivity 64%) has been obtained at 525 ° C, with a propene to oxygen ratio of 26, on a catalyst formed by Bi₄₈ZnO₇₃ with a small excess of ZnO.     

Comparison Between a Pt–Rh/Ba/Al2O3 and a Newly Formulated NOX-Trap Catalysts Under Alternate Lean–Rich Flows

In situ FT-IR spectroscopy coupled with mass spectrometry have been used to study the mechanism of nitrates formation and reduction over a common Pt–Rh/Ba/Al₂O₃ NO _x storage catalyst, compared with a different alumina-based compound.The experimental device used consists of a transmission reactor cell (having a very small dead volume) dedicated to the evolution of surface species, and of a mass spectrometer combined with a FT-IR micro-cell for gas analysis, allowing time resolved analysis in stationary and transient conditions.At the first time the nitration properties of the catalysts under a lean flow have been studied in the appropriate temperature window (473–673 K). The dynamics of nitrates formation has been pointed out, as well as the different coordination sites on the compounds surface. Then the catalysts have been alternatively exposed to rich and lean flows very close to the real exhaust composition. This has allowed the identification of reduction pathway, active sites, intermediate species and by-products for NO _X -trap reaction. In particular, we have differentiated the role of the support and of the noble metal in the mechanism, as well as of isocyanate adspecies and ammonia among the detected species. The very high NO _X storage properties and the selectivity (near 100%) in nitrogen of the newly designed catalyst have been pointed out.     

Grain-boundary sliding measurements in Al2O3 by machine vision photogrammetry

The nucleation, growth and coalescence of grain-boundary cavities is the primary damage mechanism observed during creep of structural ceramics. Furthermore, grain-boundary sliding (GBS) has been identified as the driving force process. Although the creep characteristics of structural ceramics have been extensively studied, very little is known about the details of GBS during creep and how GBS relates to cavitation kinetics. This paper presents the results of a study using a machine vision system to measure Mode II GBS displacements in a Lucalox Al₂O₃. Specifically, sliding displacements as large as 0.4 m were measured. The measured displacements indicate that some grain boundaries experienced shear strains and strain rates of 4200% and 2.3×10^–2 s^–1, respectively. The techniques utilized for these measurements are described in detail, and data gathered during a 2 1/2 h compressive creep test under a stress of 138 MPa at 1600 °C are presented and discussed.     

Observation of deep levels associated with dislocations in n-type Hg0.3Cd0.7Te

Deep level transient spectroscopy (DLTS) has been used to study the traps associated with dislocations in n-type Hg_0.3Cd_0.7Te. Dislocations have been generated by ion implantation at high fluence. Two of the broadened lines (E1=E _c–0.22eV and E1=E _c–0.34eV), we have observed, show a logarithmic dependence with the filling pulse. They are characteristic of point defect clouds surrounding or generated by the dislocations. An unusual broadened line (E2=E _c–0.27eV) has also been observed, its amplitude decreases for filling pulses longer than 50 s. This can be explained by a configuration change of the defect leading to the appearance of a new DLTS line. In addition, an electron trap (EP4=E _c–0.22eV), which seems to behave like an isolated point defect, has also been found.     

The expanding small heat-shock protein family, and structure predictions of the conserved "alpha-crystallin domain"

The ever-increasing number of proteins identified as belonging to the family of small heat-shock proteins (shsps) and alpha-crystallins enables us to reassess the phylogeny of this ubiquitous protein family. While the prokaryotic and fungal representatives are not properly resolved, most of the plant and animal shsps and related proteins are clearly grouped in distinct clades, reflecting a history of repeated gene duplications. The members of the shsp family are characterized by the presence of a conserved homologous "alpha-crystallin domain," which sometimes is present in duplicate. Predictions are made of secondary structure and solvent accessibility of this domain, which together with hydropathy profiles and intron positions support the presence of two similar hydrophobic beta-sheet-rich motifs, connected by a hydrophilic alpha-helical region. Together with an overview of the newly characterized members of the shsp family, these data help to define this family as being involved as stable structural proteins and as molecular chaperones during normal development and induced under pathological and stressful conditions.     

DNA-Directed alkylating agents. 7. Synthesis, DNA interaction, and antitumor activity of bis(hydroxymethyl)- and bis(carbamate)-substituted pyrrolizines and imidazoles

A series of bis(hydroxymethyl)-substituted imidazoles, thioimidazoles, and pyrrolizines and related bis(carbamates), linked to either 9-anilinoacridine (intercalating) or 4-(4-quinolinylamino)benzamide (minor groove binding) carriers, were synthesized and evaluated for sequence-specific DNA alkylation and cytotoxicity. The imidazole and thioimidazole analogues were prepared by initial synthesis of [(4-aminophenyl)alkyl]imidazole-, thioimidazole-, or pyrrolizine dicarboxylates, coupling of these with the desired carrier, and reduction to give the required bis(hydroxymethyl) alkylating moiety. The pyrrolizines were the most reactive alkylators, followed by the thioimidazoles, while the imidazoles were unreactive. The pyrrolizines and some of the thioimidazoles cross-linked DNA, as measured by agarose gel electrophoresis. Strand cleavage assays showed that none of the compounds reacted at purine N7 or N3 sites in the gpt region of the plasmid gpt2Eco, but the polymerase stop assay showed patterns of G-alkylation in C-rich regions. The corresponding thioimidazole bis(carbamates) were more selective than the bis(hydroxymethyl) pyrrolizines, with high-intensity bands at 5'-NCCN, 5'-NGCN and 5'-NCGN sequences in the PCR stopping assay ( indicates block sites). The data suggest that these targeted compounds, like the known thioimidazole bis(carbamate) carmethizole, alkylate exclusively at guanine residues via the 2-amino group, with little or no alkylation at N3 and N7 guanine or adenine sites. The cytotoxicities of the compounds correlated broadly with their reactivities, with the bis(hydroxymethyl)imidazoles being the least cytotoxic (IC50s >1 microM; P388 leukemia) and with the intercalator-linked analogues being more cytotoxic than the corresponding minor-groove-targeted ones. This was true also for the more reactive thioimidazole bis(carbamates) (IC50s 0.8 and 11 microM, respectively), but both were more active than the analogous "untargeted" carmethizole (IC50 20 microM). The bis(hydroxymethyl)pyrrolizine analogues were the most cytotoxic, with IC50s as low as 0.03 microM.     

'98 Escherichia coli SWISS-2DPAGE database update

The combination of two-dimensional polyacrylamide gel electrophoresis (2-D PAGE), computer image analysis and several protein identification techniques allowed the Escherichia coli SWISS-2DPAGE database to be established. This is part of the ExPASy molecular biology server accessible through the WWW at the URL address http://www.expasy.ch/ch2d/ch2d-top.html . Here we report recent progress in the development of the E. coli SWISS-2DPAGE database. Proteins were separated with immobilized pH gradients in the first dimension and sodium dodecyl sulfate-polyacrylamide gel electrophoresis in the second dimension. To increase the resolution of the separation and thus the number of identified proteins, a variety of wide and narrow range immobilized pH gradients were used in the first dimension. Micropreparative gels were electroblotted onto polyvinylidene difluoride membranes and spots were visualized by amido black staining. Protein identification techniques such as amino acid composition analysis, gel comparison and microsequencing were used, as well as a recently described Edman "sequence tag" approach. Some of the above identification techniques were coupled with database searching tools. Currently 231 polypeptides are identified on the E. coli SWISS-2DPAGE map: 64 have been identified by N-terminal microsequencing, 39 by amino acid composition, and 82 by sequence tag. Of 153 proteins putatively identified by gel comparison, 65 have been confirmed. Many proteins have been identified using more than one technique. Faster progress in the E. coli proteome project will now be possible with advances in biochemical methodology and with the completion of the entire E. coli genome.