Klimacharakter und Pflanzendecke

Ohne Zusammenfassung     

Thermodynamic cycle-perturbation study of the binding of trifluoroacetyl dipeptide anilide inhibitors with porcine pancreatic elastase

The variety of results of crystallographic studies of the serine proteases complexed with isocoumarin inhibitors presents a challenging problem to modeling methods and molecular energetics. Therefore, the thermodynamic cycle-perturbation technique has been used to study a model system of elastase and two peptidic inhibitors. Using the program AMBER, the technique correctly predicts changes of the binding constants for the trifluoroacetyl dipeptide inhibitors in comparison with available experimental (kinetic and crystallographic) data. However, the absolute values obtained are shown to be sensitive to the specific electrostatic interaction potential parameters used in the simulations. The reader and user are cautioned that thermodynamic cycle-perturbation results may be too optimistic by underestimating the accuracy of free energy values. This is especially a matter of concern for those cases where a direct comparison with experimental values is not possible, viz., (1) the stimulation of binding of novel compounds, (2) structurally uncertain binding sites, or (3) structurally different binding modes. With our best 4-31G* ESP (electrostatic potential) charges we were able to reproduce experimentally determined free energy differences (delta delta A) with an accuracy of about 1.5 kcal/mol. Dynamically induced structural changes in the binding site of elastase, and particularly changes in hydrogen-bond patterns of the binding site, are also reported.     

Bacteriophage-resistance mechanisms examined by transfection of Lactococcus lactis subsp. lactis 4513-5 mediated by high voltage electroporation

Summary Phage adsorption tests and transfection by electroporation were carried out to decide whether phage-resistance in Lactococcus lactis subsp. lactis strain 4513-5 is based on intracellular or extracellular mechanisms. Using high voltage (12.5 kV/cm) electroporation, untreated phage DNA was introduced into phage-sensitive and phage-resistant cells. Since phages showed low adsorption frequencies on resistant bacteria, resistance is localized in the cell wall preventing phage DNA from entering the cell. This is the only mechanism responsible for the resistance of L. lactis subsp. lactis 4513-5 against its homologous phage P4513-K12 and non-homologous phages P05M-13 and P05M-47, but not against phage P530-7 and phage P530-12. In the case of the latter two phage strains, intracellular resistance mechanisms are involved and discussed.     

Studies on prolysostaphin processing and characterization of the lysostaphin immunity factor (Lif) of Staphylococcus simulans biovar staphylolyticus

Lysostaphin is an extracellular glycylglycine endopep-tidase produced by Staphylococcus simulans biovar staphylolyticus ATCC1362 that lyses staphylococcal cells by hydrolysing the polyglycine interpeptide bridges of the peptidoglycan. Renewed analysis of the sequence of the lysostaphin gene (Iss), and the sequencing of the amino-terminus of purified prolysostaphin and of mature lysostaphin revealed that lysostaphin is organized as a preproprotein of 493 amino acids (aa), with a signal peptide consisting of 36 aa, a propeptide of 211 aa from which 195 aa are organized in 15 tandem repeats of 13 aa length, and a mature protein of 246 aa. Prolysostaphin is processed in the culture supernatant of S. simulans biovar staphylolyticus by an extracellular cysteine protease. Although prolysostaphin was staphylolytically active, the mature lysostaphin was about 4.5-fold more active. The controlled expression in Staphylococcus carnosus of Iss and Iss with deletions in the prepropeptide region indicated that the tandem repeats of the propeptide are not necessary for protein export or activation of Lss, but keep Lss in a less active state. Intracellular expressed pro- and mature lysostaphin exert staphy-lolytic activity in cell-free extracts, but do not affect growth of the corresponding clones. We characterized a lysostaphin immunity factor gene (lif) which is located in the opposite direction to Iss. The expression of lif in S. carnosus led to an increase in the serine/glycine ratio of the interpeptide bridges of peptidoglycan from 2 to 35%, suggesting that lysostaphin immunity depends on serine incorporation into the interpeptide bridge. If, in addition to lif, Iss is co-expressed the serine/glycine ratio is further increased to 58%, suggesting that Lss selects for optimal serine incorporation. Lif shows similarity to FemA and FemB     

Trace fossils from Lower Miocene (Ottnangian) molasse deposits of Upper Austria

Lower Miocene siliciclastic sediments of the Vöckla Schichten and Atzbacher Sande, Austria, contain a shallow-water trace-fossil assemblage of the Cruziana ichnofacies includingSkolithos isp.,Planolites ? beverleyensis, Ophiomorpha annulata, O.nodosa, Rosselia socialis, Cylindrichnus concentricus, Scolicia isp., andBichordites monastiriensis. The ichnogenusRosselia and the ichnospeciesRosselia socialis are revised. Analysis ofScolicia isp. andB. monastiriensis provides new information about their morphology and ichnotaxonomy.     

Somatic polyploidy in extraembryonic membranes of the snake,Elaphe guttata

Summary Video-densitometric DNA measurements of Feulgenstained tissues of 42 day old eggs of the corn snake,Elaphe g. guttata (Columbridae, Serpentes), revealed a basic DNA content of 2C=2.17 pg, with somatic polyploidy in the allantois, the chorioallontois, the yolk sac, and other extraembryonic membranes. The maximum value determined was 128C (in binucleate cells 2×128C) at the distal pole of the egg. This is the first report of somatic polyploidy in a snake, and one of the first in reptiles in general.     

Intra- and interspecific host discrimination in Asobara (Hymenoptera) larval endo-parasitoids of Drosophilidae: Comparison between closely related and less closely related species

Host discrimination studies were conducted with different species of Asobara, which are larval endo-parasitoids of Drosophilidae. Results indicated variable host discrimination which depended on the relatedness of the species. The closely related sibling species Asobara tabida (Nees) and A. rufescens (Foerster) were not only capable of intraspecific discrimination, but also avoided multiparasitism by discriminating between unparasitized host larvae and larvae previously parasitized by females of the other species. This ability to discriminate interspecifically does not seem functional as each species occupies its own microhabitat. As it was shown to be absent in less closely related Asobara species we concluded that interspecific discrimination by A. tabida and A. rufescens was due to their close relationship.     

Identification of substrate and effector binding sites of phosphoenolpyruvate carboxylase from Crassula argentea. A possible role of phosphoenolpyruvate as substrate and activator

Phosphoenolpyruvate carboxylase (EC 4.1.1.31) purified from leaves of the crassulacean acid metabolism plant (Crassula argentea) was chemically modified by the specific arginyl reagent 2,3-butanedione. Modification resulted in enzyme inactivation which followed pseudo first-order kinetics. Participation of arginyl residues involved in the binding of or response to both phosphoenolpyruvate and malate, respectively, was established. Inactivation and protection studies suggest the presence of three sites involved in the binding of the substrate, phosphoenolpyruvate, the activator, glucose 6-phosphate, and the inhibitor, malate. Studies using both fluorescence measurements of binding and steady-state kinetic methods indicate that phosphoenolpyruvate can bind both to the active site and to the activator site. Evidence for stimulation of the activity of phosphoenolpyruvate carboxylase upon the binding of substrate to the activation site was provided by kinetic studies using AMP, previously shown to be a specific ligand for the activation site.