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.     

Die Formbildungsmuster und das Wirbelphänomen in der Cölombewimperung von Nephthys

Ohne Zusammenfassung     

Skull molding caps: an adjunct to craniosynostosis surgery

External cranial vault molding using dynamic splinting is an adjunct to surgery in the treatment of craniosynostosis skull deformities. The skull molding cap not only maintains desired skull form, but also provides further active molding to normalize skull shape. Dynamic skull remodeling from these devices occurs primarily by translational movements of bone. Traction and compression result in bony repositioning which allows further reshaping as the osteoblasts and osteoclasts respond to these stresses. Three basic designs have been described. In practice, each one must be modified to meet individual needs, and adaptations are made according to established principles of dynamic splinting.     

Light-regulated methylation of chloroplast proteins

Protein carboxyl methyltransferases, which catalyze transfer of methyl groups from S-adenosyl-L-methionine to the free carboxyl groups of acidic amino acids in proteins, can be divided into two classes based on several characteristics, such as the stoichiometry of substrate protein methylation, base stability of the incorporated methyl group, specificity for substrate, and participation in a regulatory system with which methylesterases are associated. The presence of such an enzyme in a photosynthetic system was demonstrated in the present work. The extent of methylation of chloroplast proteins was stimulated 30% by light and then decreased by the same amount in the presence of the electron transport inhibitor 3-(3',4'-dichlorophenyl)-1', 1'-dimethylurea or uncouplers of phosphorylation, indicating a dependence of the methyltransferase activity on photosynthetic electron transport and the trans-membrane delta pH. The light-independent, as well as the light-dependent, activity is probably of chloroplast origin since the extent of light stimulation in the purified thylakoid membranes and the stromal fraction was similar, and at low concentrations of S-adenosyl-L-methionine the small subunit of ribulose-1,5-bisphosphate carboxylase:oxygenase was found to be the predominant substrate. The labeling pattern of chloroplast proteins and labeling of an exogenous nonchloroplast protein indicated that the methyltransferase activity was not substrate-specific, although at low concentrations of the methyl donor, the small subunit of ribulose-1,5-bisphosphate carboxylase:oxygenase was labeled almost exclusively. Based on the low stoichiometry (less than 100 pmol/mg protein) of the methylation, its base lability, irreversibility, and the lack of substrate specificity except at very low concentrations of methyl donor, it was inferred that the chloroplast methyltransferase is best classified as a class II system that may function as part of a repair mechanism to replace racemized amino acids.     

The nature of the neutral Na+−Cl−-coupled entry at the apical membrane of rabbit gallbladder epithelium: II. Na+−Cl− symport is independent of K+

Summary In the epithelium of rabbit gallbladder, in the nominal absence of bicarbonate, intracellular Cl^– activity is about 25mm, about 4 times higher than intracellular Cl^– activity at the electrochemical equilibrium. It is essentially not affected by 10^–4 m acetazolamide and 10^–4 m 4-acetamido-4-isothiocyanostilbene-2,2-disulfonate (SITS) even during prolonged exposures; it falls to the equilibrium value by removal of Na⁺ from the lumen without significant changes of the apical membrane potential difference. Both intracellular Cl^– and Na⁺ activities are decreased by luminal treatment with 25mm SCN^–; the initial rates of change are not significantly different. In addition, the initial rates of change of intracellular Cl^– activity are not significantly different upon Na⁺ or Cl^– entry block by the appropriate reduction of the concentration of either ion in the luminal solution. Luminal K⁺ removal or 10^–5 m bumetanide do not affect intracellular Cl^– and Na⁺ activities or Cl^– influx through the apical membrane. It is concluded that in the absence of bicarbonate NaCl entry is entirely due to a Na⁺–Cl^– symport on a single carrier which, at least under the conditions tested, does not cotransport K⁺.     

The nature of the neutral Na+−Cl−-coupled entry at the apical membrane of rabbit gallbladder epithelium: I. Na+/H+, Cl−/HCO 3 − double exchange and Na+−Cl− symport

Summary Cl^– influx at the luminal border of the epithelium of rabbit gallbladder was measured by 45-sec exposures to³⁶Cl^– and³H-sucrose (as extracellular marker). Its paracellular component was evaluated by the use of 25mm SCN^– which immediately and completely inhibits Cl^– entry into the cell. Cellular influx was equal to 16.7eq cm^–2 hr^–1 and decreased to 8.5eq cm^–2 hr^–1 upon removal of HCO ₃ ^– from the bathing media and by bubbling 100% O₂ for 45 min. When HCO ₃ ^– was present, cellular influx was again about halved by the action of 10^–4 m acetazolamide, 10^–5 to 10^–4 m furosemide, 10^–5 to 10^–4 m 4-acetamido-4-isothiocyanostilbene-2,2-disulfonate (SITS), 10^–3 m amiloride. The effects of furosemide and SITS were tested at different concentrations of the inhibitor and with different exposure times: they were maximal at the concentrations reported above and nonadditive. In turn, the effects of amiloride and SITS were not additive. Acetazolamide reached its maximal action after an exposure of about 2 min. When exogenous HCO ₃ ^– was absent, the residual cellular influx was insensitive to acetazolamide, furosemide and SITS. When exogenous HCO ₃ ^– was present in the salines, Na⁺ removal from the mucosal side caused a slow decline of cellular Cl^– influx; conversely, it immediately abolished cellular Cl^– influx in the absence of HCO ₃ ^– . In conclusion, about 50% of cellular influx is sensitive to HCO ₃ ^– , inhibitable by SCN^–, acetazolamide, furosemide, SITS and amiloride and furthermore slowly dependent on Na⁺. The residual cellular influx is insensitive to bicarbonate, inhibitable by SCN^–, resistant to acetazolamide, furosemide, SITS and amiloride, and immediately dependent on Na⁺. Thus, about 50% of apical membrane NaCl influx appears to result from a Na⁺/H⁺ and Cl^–/HCO ₃ ^– exchange, whereas the residual influx seems to be due to Na⁺–Cl^– contranport on a single carrier. Whether both components are simultaneously present or the latter represents a cellular homeostatic counterreaction to the inhibition of the former is not clear.     

High-Efficiency Conversion of Pyruvate to Acetoin by Lactobacillus plantarum during pH-Controlled and Fed-Batch Fermentations

The influence of pH on the type and concentration of metabolites produced from pyruvate by Lactobacillus plantarum ATCC 8014 was examined in pH-controlled fermentors at pH values of 4.5 to 6.5. Specific growth rates, cell dry weights, and diacetyl concentrations were highest at pH 5.5, with values of 0.78 h⁻¹, 190 mg/liter, and 1.2 mM, respectively. While the conversion efficiency (millimoles of acetoin formed per millimoles of pyruvate utilized) was highest (94.6%) at pH 4.5, acetoin levels were similar (20 mM) between pH 4.5 and 5.5. Feeding stationary-phase cells exogenous pyruvate increased acetoin levels to 78 mM.     

Isolation of apical plasma membrane in rabbit gallbladder epithelium by Percoll density gradient centrifugation

The apical membranes of rabbit gallbladder epithelial cells were isolated by treating the homogenate with Ca2+ or Mg2+ and centrifuging the suspension in Percoll gradient. In this way brush-border membranes were obtained with enrichment factors ranging between 10 and 20 and yields of 15-30%. A second method is described with which membranes were isolated, without any preliminary treatment, first by differential centrifugation, then with Percoll gradient; the final membrane enrichment was over 15, however the yield was very low (3%). Many possible enzymatic markers of the apical plasma membrane were investigated: L-gamma-glutamyltransferase, alkaline phosphatase, leucine aminopeptidase, sucrase. The first appears to be that of choice. Apical membrane fraction could be also evidenced by autofluorescence or by labeling with Lotus tetragonolobus lectin. Preliminary experiments showed that apical plasma membranes isolated in this way form vesicles.