Bilayer stabilizing peptides and the inhibition of viral infection: antimeasles activity of carbobenzoxy-Ser-Leu-amide

A number of carbobenzoxy-dipeptide-amides raise the bilayer to hexagonal phase transition temperature of dielaidoylphosphatidylethanolamine (stabilizes the bilayer). The potency of the peptides in stabilizing the bilayer phase is Z-Tyr-Leu-NH₂= Z-Gly-Phe-NH₂>Z-Ser-Leu-NH₂>Z-Gly-Leu-NH₂>Z-Gly-Gly-NH₂. A linear correlation was found between the respective HPLC retention time parameterk for the peptide and the slope of the bilayer stabilization curve determined with model membranes by differential scanning calorimetry. One dipeptide, Z-Ser-Leu-NH₂, reduces measles virus cytopathic effect (CPE) in Vero cells. The mechanism by which this peptide reduces the CPE is not known, although some peptides which raise the bilayer to hexagonal phase transition temperature of phospholipids inhibit membrane fusion.Abbreviations Z carbobenzoxy - DEPE dielaidoylphosphatidylethanolamine - DSC differential scanning calorimetry - HPLC high pressure liquid chromatography - CPE cytopathic effect To whom correspondence should be addressed.     

In vitro depolymerization dynamics of brain endogenous microtubules

A subcellular fraction containing fragments of endogenous microtubules stabilized in 50% glycerol was separated by diferential centrifugation of rat brain homogenates. The pellets were suspended in glycerol-deficient media, and microtubule depolymerization was monitored by measuring the decrease of sedimentable tubulin. Concomitantly, the number and size of microtubules in the suspensions were followed via electron microscopy. Depolymerization was accompanied by a proportional decrease in the number of microtubules, whereas the average size did not change significantly. After approximately 20 min, a subpopulation of microtubules became stable and did not suffer further depolymerization. These results indicate that upon dilution some microtubules completely depolymerize, whereas others remain stable in the glycerol-deficient medium. The degree of depolymerization depended on both the volume of the resuspension media and on the final glycerol concentration. The results suggest that the depolymerization of the remaining microtubules is prevented by stabilizing factors released from depolymerizing microtubules. Tubulin dimers are not one of these factors, since depolymerization was not altered by the addition of colchicine or by changing the concentration of free tubulin in the medium.     

人工樟子松—差不嗄蒿植被及其固沙作用

植物固沙是整治沙漠和沙漠化土地的一种有效措施。人工植被的建立是植物固沙的必然结果。人工植被的演替、稳定性及其对环境的影响直接关系到流沙的固定程度。因此,本文旨在探讨人工樟子松(Pinus sylvestris var.     

Stabilization of cortical microtubules by the cell wall in cultured tobacco cells

Cortical microtubules (MTs) in protoplasts prepared from tobacco (Nicotiana tabacum L.) BY-2 cells were found to be sensitive to cold. However, as the protoplasts regenerated cell walls they became resistant to cold, indicating that the cell wall stabilizes cortical MTs against the effects of cold. Since poly-l-lysine was found to stabilize MTs in protoplasts, we examined extensin, an important polycationic component of the cell wall, and found it also to be effective in stabilizing the MTs of protoplasts. Both extensin isolated from culture filtrates of tobacco BY-2 cells and extensin isolated in a similar way from cultures of tobacco XD-6S cells rendered the cortical MTs in protoplasts resistant to cold. Extensin at 0.1 mg·ml⁻¹ was as effective as the cell wall in this respect. It is probable that extensin in the cell wall plays an important role in stabilizing cortical MTs in tobacco BY-2 cells.     

Antimicrobial susceptibility of non-O1 Vibrio cholerae isolated from wastewater stabilization ponds in Marrakesh,Morocco

The 365 strains of Vibrio cholerae, isolated in Marrakesh from raw sewage and stabilization pond effluent, were all identified as non-O1 Vibrio cholerae. When tested for their susceptibilities to ampicillin, amoxicillin, cephalothin, streptomycin, novobiocin, chloramphenicol, nalidixic acid and trimethoprim-sulphamethoxazole, 13% of the strains from raw sewage and 20% of those from stabilization pond effluent were found to be resistant to one or more of the antibiotics. There were no significant differences, in terms of drug resistance, between isolates from the new sewage and those from the ponds' effluent.The authors are with the Université Cadi Ayyad, Faculté des Sciences Semialia, Département de Biologie, Laboratoire de Microbiologie, BP S/15, Marrakesh, Morocco     

The adsorptive immobilization of phospholipids D mediated by calcium ions

Immobilization of phospholipase D from cabbage was studied with the aim of stabilizing the enzyme for its use in synthesis of phospholipids. It was shown that phospholipase D can be immobilized by adsorption to polymeric carriers containing long chain anchor groups such as octadecyl, octyl, or other alkyl residues. Starting from the crude enzyme, phospholipase D activity is preferentially bound (up to 100%) in competition with contaminating proteins. A prerequisite of high binding rates is the presence of calcium ions, which play a mediating role in the adsorption process. The maximum activity of the carrier-enzyme complexes depends upon the calcium concentration in the immobilization process and the carrier material (>/=10mM CaCl(2) with octadecyl-Si40, >/=40 mM CaCl(2) with octyl-sepharose and butyl-fractogel). Immobilization of phospholipase D to octyl-sepharose was shown to result in a distinctly increased storage stability and an enlarged pH-optimum range for the catalytic activity. Operational stability of different phospholipase D-carrier complexes was compared. (c) 1993 Wiley & Sons, Inc.     

Dominant role of local dipoles in stabilizing uncompensated charges on a sulfate sequestered in a periplasmic active transport protein.

Electrostatic interactions are among the key factors determining the structure and function of proteins. Here we report experimental results that illuminate the functional importance of local dipoles to these interactions. The refined 1.7-A X-ray structure of the liganded form of the sulfate-binding protein, a primary sulfate active transport receptor of Salmonella typhimurium, shows that the sulfate dianion is completely buried and bound by hydrogen bonds (mostly main-chain peptide NH groups) and van der Waals forces. The sulfate is also closely linked, via one of these peptide units, to a His residue. It is also adjacent to the N-termini of three alpha-helices, of which the two shortest have their C-termini "capped" by Arg residues. Site-directed mutagenesis of the recombinant Escherichia coli sulfate receptor had no effect on sulfate-binding activity when an Asn residue was substituted for the positively charged His and the two Arg (changed singly and together) residues. These results, combined with other observations, further solidify the idea that stabilization of uncompensated charges in a protein is a highly localized process that involves a collection of local dipoles, including those of peptide units confined to the first turns of helices. The contribution of helix macrodipoles appears insignificant.     

Effect of Planting Unit Size and Sediment Stabilization on Seagrass Transplants in Western Australia

Abstract The effect of increasing planting unit size and stabilizing sediment was examined for two seagrass planting methods at Carnac Island, Western Australia in 1993. The staple method (sprigs) was used to transplant Amphibolis griffithii (J. M. Black) den Hartog and the plug method was used to transplant A. griffithii and Posidonia sinuosa Cambridge and Kuo. Transplant size was varied by increasing the number of rhizomes incorporated into a staple and increasing the diameter of plugs. Planting units were transplanted into bare sand, back into the original donor seagrass bed, or into a meadow of Heterozostera tasmanica, which is an important colonizing species. Sprigs of A. griffithii were extracted from a monospecific meadow; tied into bundles of 1, 2, 5, and 10 rhizomes; and planted into unvegetated areas. Half the units were surrounded by plastic mesh and the remainder were unmeshed. All treatments were lost within 99 days after transplanting, and although larger bundles survived better than smaller ones, no significant differences could be attributed to the effects of mesh or sprig size. Plugs of P. sinuosa and A. griffithii were extracted from monospecific meadows using polyvinyl chloride pipe of three diameters, 5, 10, and 15 cm, and planted into unvegetated areas nearby. Half the units were surrounded by plastic mesh and the remainder were unmeshed. Posidonia sinuosa plugs were also placed within a meadow of H. tasmanica (Martens ex Aschers.) den Hartog. Only 60% of A. griffithii plug sizes survived 350 days after transplanting back into the donor bed; however, survival of transplants at unvegetated areas varied considerably, and analysis of variance indicated a significant two‐way interaction between treatment and plug size. Transplants survived better when meshed (90% survived) and survival improved with increasing plug size. Posidonia sinuosa transplants survived poorly (no plugs survived beyond 220 days in bare or meshed treatments) regardless of size. Survival of 10‐ and 15‐cm plugs was markedly better than the 5‐cm plugs in vegetated areas, including the H. tasmanica meadow. The use of large seagrass plugs may be appropriate for transplantation in high‐energy wave environments.     

多组多滞后区间系数定常非线性关联控制大系统的结构与关联鲁棒镇定(I)

建立了多组多滞后区间系数定常非线性控制系统的结构概念,采用鲁棒镇定的等价法,给出了具有扰动结构参数的多组多滞后区问系数定常非线性关联控制大系统的结构与关联鲁棒镇定,同时给出了扰动参数与滞后非线性项界线的估价公式。