Monensin inhibits the secretion of α-amylase but not polysaccharide slime from seedling tissues ofZea mays

Summary The effect of monensin on polysaccharide slime secretion by root tips of corn (Zea mays) was studied. Various treatment times and ionophore concentrations were tested: none resulted in inhibition of slime secretion. Because monensin changes the pH of the medium, its effect was also monitored in strongly buffered media and at different pH's. Even in such media, monensin did not inhibit slime secretion. We also measured the effect of the drug after a pulse with [³H]fucose or a pulse followed by a chase. The amount of labeled slimed secreted was not altered by the ionophore. However, 10M monensin affected the development of root tips and drastically reduced their growth. We showed that monensin inhibits the secretion of -amylase by the scutellum of the same plantlet. The importance of the nature of the secretory compound in relation to monensin inhibition of its secretion is discussed.Abbrevations Hepes N-2-hydroxyethylpiperazine-N-2-ethane-sul-fonic acid - Mes 2-(N-morpholino)ethane-sulfonic acid     

Some biochemical properties of an acyclic oligonucleotide analogue. A plausible ancestor of the DNA?

As acyclic oligonucleotides have been suggested as a primitive model of DNA or RNA in prebiotic times, we compared some biochemical properties of these analogues to that of natural ones. Firstly, an acyclic analogue of deoxyribonucleoside triphosphates was tested as a potential substrate of enzymes intervening in nucleic acids synthesis. GlyTTP, a dTTP analogue with a missing 2-methylene group is notaccepted as a substrate by either DNA polymerase or deoxynucleotidyl terminal transferase (TdT). Secondly, themodified dodecathymidylate (GlyT)₁₂, the racemic acyclic sugar analogue of (dT)₁₂, proved to be anefficient primer for DNA polymerase and TdT, though the associative properties of (GlyT)₁₂ are very weak as shown by UV spectroscopy in phosphate buffer without magnesium chloride. But (GlyT)₁₂ has the advantage to be 500-times more stable against hydrolysis by snake venom phosphodiesterase than the corresponding oligothymidylate.     

In vitro study of the proteolytic activity of rumen anaerobic fungi

Abstract To better define the antigenic structure of the outer cell membranes of Legionellae, a panel of 6 monoclonal antibodies was raised against partially purified outer membranes of Legionella pneumophila serogroup 1, Corby strain. This study describes the purification and characterization of one of these monoclonal antibodies reacting with a 135-kDa protein, which was shown to be common to all 14 serogroups of Legionella pneumophila . It shows no cross-reactivity with 20 other Legionella species, or 9 other Gram-negative species tested by SDS-PAGE and Western blotting procedures. The epitope would appear to be predominantly surface exposed and, from preliminary detergent extraction studies, not peptidoglycan-associated.     

Design of new inhibitors specific to the adenosine triphosphate binding site of DNA topoisomerases II

Summary DNA topoisomerases II are involved in the segregation of chromosomes which occurs after DNA replication. These enzymes proceed by nicking and resealing of a phosphodiester bond of the DNA double helix and require the hydrolysis of ATP into ADP and inorganic phosphate. Studies of ATP hydrolysis showed specific properties according to the source of isolation of the enzymes, suggesting the existence of an evolution of the ATP binding site of DNA topoisomerases II. In order to study this evolution, two experimental strategies were followed, first of all an analysis of the topography of the ATP binding site by forming UV crosslinks between ATP and the enzymes, and second the effects of new inhibitors.     

Effect of Bacillus thuringiensis Cry1 Toxins in Insect Hemolymph and Their Neurotoxicity in Brain Cells of Lymantria dispar

Little information is available on the systemic effects of Bacillus thuringiensis toxins in the hemocoel of insects. In order to test whether B. thuringiensis-activated toxins elicit a toxic response in the hemocoel, we measured the effect of intrahemocoelic injections of several Cry1 toxins on the food intake, growth, and survival of Lymantria dispar (Lepidoptera) and Neobellieria bullata (Diptera) larvae. Injection of Cry1C was highly toxic to the Lymantria larvae and resulted in the complete inhibition of food intake, growth arrest, and death in a dose-dependent manner. Cry1Aa and Cry1Ab (5 μg/0.2 g [fresh weight] [g fresh wt]) also affected growth and food intake but were less toxic than Cry1C (0.5 μg/0.2 g fresh wt). Cry1E and Cry1Ac (5 μg/0.2 g fresh wt) had no toxic effect upon injection. Cry1C was also highly toxic to N. bullata larvae upon injection. Injection of 5 μg/0.2 g fresh wt resulted in rapid paralysis, followed by hemocytic melanization and death. Lower concentrations delayed pupariation or gave rise to malformation of the puparium. Finally, Cry1C was toxic to brain cells of Lymantria in vitro. The addition of Cry1C (20 μg/ml) to primary cultures of Lymantria brain cells resulted in rapid lysis of the cultured neurons.     

Systemic Responses in Arabidopsis thaliana Infected and Challenged with Pseudomonas syringae pv syringae

Attack of plants by necrotizing pathogens leads to acquired resistance to the same or other pathogens in tissues adjacent to or remotely located from the site of initial attack. We have used Arabidopsis thaliana inoculated with the incompatible pathogen Pseudomonas syringae pv syringae on the lower leaves to test the induction of systemic reactions. When plants were challenged with Pseudomonas syringae pv syringae in the upper leaves, bacterial titers remained stable in those preinfected on the lower leaves. However, there was a distinct decrease in symptoms that correlated with a local and systemic increase in salicylic acid (SA) and in chitinase activity. Peroxidase activity only increased at the site of infection. No changes in catalase activity were observed, either at the local or at the systemic level. No inhibition of catalase could be detected in tissue in which the endogenous levels of SA were elevated either naturally (after infection) or artificially (after feeding SA to the roots). The activity of catalase in homogenates of A. thaliana leaves could not be inhibited in vitro by SA. SA accumulation was induced by H2O2 in leaves, suggesting a link between H2O2 from the oxidative burst commonly observed during the hypersensitive reaction and the induction of a putative signaling molecule leading to system acquired resistance.     

Interactions of HIV-1 and HIV-2 envelope glycoproteins with sulphated polysaccharides and mannose-6-phosphate

Envelope glycoproteins of human immunodeficiency viruses (HIV-1and HIV-2) can interact with high-mannose glycans and with themannosyl or N-acetylglucosaminyl core of complex-type oligosaccharidicstructures. HIV-1 glycoproteins also specifically bind sulphatedpolysaccharides such as dextran sulphate (DS) and heparin. Here,we show that the latter property is shared by HIV-2 recombinantgp140 (rgpl40) precursor glycoprotein. Binding of rgpl40 andof corresponding rgp160 of HIV-1 to heparin- and DS-substituted(sulphated dextran beads; SDB) affinity matrices was inhibitedby the soluble specific ligand and also by fetuin, asialofetuinor the anionic simple carbohydrate derivative manncsse-6-phosphate(M6P). Interaction of HIV-1 rgpl20 subunit with the two affinitymatrices was also inhibited by M6P, but only rgpl20 bindingto heparin-agarose, and not that to SDB, was affected by fetuinand asialofetuin. These results suggest that HIV-1 and HIV-2envelope glycoproteins presumably display different sulphatedpolysaccharide and carbohydrate recognition sites. Some of thesemay be common or in close proximity: with respect to rgpl60,for example, the sites may be common on the gp41 moiety and/orin a region of gp120 which would be more accessible when expressedon rgpl60 than on processed gpl20, while they may be distincton the cleaved gpl20 subunit. Finally, because M6P is a markerof lysosomal enzymes, we verified that HIV-1 and HIV-2 envelopeglycoproteins could specifically bind in a M6P-inhibitable mannerto a representative lysosomal enzyme, bovine liver ß-glucuronidasecoupled to agarose, suggesting that they may possibly interferewith lysosomal enzyme sorting in HIV-infected cells. env glycoproteins HIV lectin mannose-6-phosphate sulphated polysaccharides