Side-chain control of beta-peptide secondary structures.

As one of the most important families of non-natural polymers with the propensity to form well-defined secondary structures, the beta-peptides are attracting increasing attention. The compounds incorporating beta-amino acid residues have found various applications in medicinal chemistry and biochemistry. The conformational pool of beta-peptides comprises several periodic folded conformations, which can be classified as helices, and nonpolar and polar strands. The latter two are prone to form pleated sheets. The numerous studies that have been performed on the side-chain dependence of the stability of the folded structures allow certain conclusions concerning the principles of design of the beta-peptide foldamers. The folding propensity is influenced by local torsional, side-chain to backbone and long-range side-chain interactions. Although beta-peptide foldamers are sensitive to solvent, the systematic choice of the side-chain pattern and spatiality allows the design of the desired specific secondary structure. The application of beta-peptide foldamers may open up new directions in the synthesis of highly organized artificial tertiary structures with biochemical functions.     

Geographische Herkunft und Anpassung beim Apfel

Zusammenfassung In den Jahren 1961 und 1962 wurden Untersuchungen mit Hilfe der Exosmose-Methode durchgeführt, um sich über die Frostresistenz von nahezu 100 Apfelsorten zu orientieren. Die Versuchsergebnisse (ausgedrückt in RLF-Werten, d. h. als Proportion des elektrolytischen Widerstandes zwischen den Kontrollen und den kältebehandelten Pflanzenteilen) zeigen gute Übereinstimmung mit den Resultaten anderer Härtebeurteilungsmethoden, z. B. mit den Gefrierversuchen in Gefrierkammern und mit den amerikanischen, deutschen und schweidischen Freilandbeobachtungen. Die berechneten Korrelationskoeffizienten gaben Werte von r=>+0,750 mit einer statistischen Sicherheit von P=<0,001. Es gibt jedoch Sorten, welche sich unter den verschiedenen Versuchsbedingungen nicht gleichartig verhielten. In diese Gruppe gehören die Sorten Goldparmäne, James Grieve, Lanes Prince Albert, Schöner aus Nordhausen, Slava Petersburga und Transparente de Croncels. Der Zusammenhang zwischen der geographischen Herkunft und der Frostresistenz ist augenfällig. Die durchschnittlichen RLF-Werte der frostempfindlichen oder sehr frostempfindlichen französischen Sorten liegen bei ungefähr 150, die der finnischen und baltischen frostharten Sorten dagegen unter 110. Die Rangordnung der verschiedenen Klimagebiete erfolgte entsprechend der geographischen Lage. Es gab Sorten, die der allgemeinen Tendenz nicht folgten und sich abweichend verhielten. Hierzu gehören: Transparente de Croncels, (Frankreich), Wealthy (USA), Cox Pomona und Ribston (Großbritannien). Über eine wesentlich schlechtere Resistenz, als auf Grund des Ursprungsgebietes zu erwarten war, verfügt Ontario (Kanada).     

Detection of double-stranded RNA molecules and virus-like particles in different Mucor species

The presence of double-stranded RNA elements was examined in 123 strains representing 18 Mucor species. These genetic elements were found to be present in 6 strains: 1 M. aligarensis, 1 M. hiemalis, 2 M. corticolus, 1 M. mucedo and 1 M. ramannianus. Electrophoretic separation of the nucleic acids revealed 4 different RNA patterns, with 1 to 5 discrete dsRNA bands. The molecular weights corresponding to these bands were 1.42–4.15 × 10⁶ D. Using electronmicroscopy, for the first time the presence of virus like particles in Mucor species has been revealed.     

Different cis-Regulatory DNA Elements Mediate Developmental Stage- and Tissue-specific Expression of the Human COL2A1 Gene in Transgenic Mice

Expression of the type II collagen gene (human COL2A1, mouse Col2a1) heralds the differentiation of chondrocytes. It is also expressed in progenitor cells of some nonchondrogenic tissues during embryogenesis. DNA sequences in the 5′ flanking region and intron 1 are known to control tissue-specific expression in vitro, but the regulation of COL2A1 expression in vivo is not clearly understood. We have tested the regulatory activity of DNA sequences from COL2A1 on the expression of a lacZ reporter gene in transgenic mice. We have found that type II collagen characteristic expression of the transgene requires the enhancer activity of a 309-bp fragment (+2,388 to +2,696) in intron 1 in conjunction with 6.1-kb 5′ sequences. Different regulatory elements were found in the 1.6-kb region (+701 to +2,387) of intron 1 which only needs 90-bp 5′ sequences for tissue-specific expression in different components of the developing cartilaginous skeleton. Distinct positive and negative regulatory elements act together to control tissue-specific transgene expression in the developing midbrain neuroepithelium. Positive elements affecting expression in the midbrain were found in the region from −90 to −1,500 and from +701 to +2,387, whereas negatively acting elements were detected in the regions from −1,500 to −6,100 and +2,388 to +2,855.     

Application of a thermally-reversible polymer-antibody conjugate in a novel membrane-based immunoassay.

We have developed a novel method to immobilize antibodies onto a cellulose acetate membrane using a conjugate of an N-isopropylacrylamide polymer covalently bound to the antibody. When compared with the unconjugated antibody, over 30-fold increase in retention of the antibody on the membrane was observed when it was conjugated to poly (N-isopropylacrylamide). Studies of the polymer-membrane interaction suggest a combination of hydrophobic and ionic forces, especially the former, is responsible for the high retention. We applied this novel immobilization technology in the development of a membrane-based immunoassay.     

Primary sequence of duck metallothionein

Only one metallothionein appears in domesticated duck upon zinc induction. The complete amino acid sequence has been elucidated. This metallothionein has the same sequence as the chicken metallothionein, as determined by chemical sequencing of overlapping peptides produced by selective proteinase digestion and confirmed by mass spectrometry. The observation that animals of divergent origins share a common gene product presents an example of extreme conservation of a stress-inducible protein.     

Selection of tumor cell variants for resistance to tumor necrosis factor also induces a form of pleiotropic drug resistance

Summary This study has addressed the question of whether there may be some common mechanism underlying the induction or expression of acquired cytokine and drug resistance in a tumor cell line. This study employed the tumor-necrosis-factor(TNF)-sensitive U937 tumor cell line as a model system to determine if selection of a tumor cell variant for cytokine resistance would also result in drug resistance and vice versa. Variants were selected by culturing in the presence of purified recombinant TNF or a mixed-lymphokine-containing supernatant derived from concanavalin-A-stimulated peripheral blood lymphocytes. The resulting variants were resistant not only to TNF, but also to certain chemotherapeutic drugs. The variants were most resistant to colchicine and theVinca alkaloids, requiring drug concentrations 50- to 5000-fold higher to mediate levels of cytotoxicity comparable to that seen with the parental U937. The variants were moderately resistant to cycloheximide, actinomycin D, and mitomycin C. In contrast, these lines were relatively sensitive to doxorubicin or daunomycin. This phenomenon was not unique to U937 cells since we obtained a similar pattern of drug resistance by selecting TNF-resistant variants of the WEHI-164 tumor cell line. The cytokine-selected U937 variants were still lysed by NK cells, although they were somewhat less sensitive than the parental U937. Both variants were relatively resistant to lysis by activated macrophages, probably because of their TNF resistance. In an alternative selection procedure, U937 variants were derived by culturing in the presence of increasing concentrations of colchicine. The resulting variants were relatively resistant to TNF, providing further support for the existence of some common mechanism operating in induction or expression of acquired cytokine and drug resistance. The resistance mechanism apparently does not involve the P glycoprotein since the cytokine-selected U937 variants do not overexpress the mdr gene. This study has demonstrated that selection of TNF-resistant variants results in coexpression of a unique form of drug resistance that is characterized by resistance to microtubule-active drugs but not to the anthracycline antibiotics and is not associated with overexpression of the mdr gene.This work was supported by grant CA 47 669-01 awarded by the National Cancer Institute Nomenclature of variants: U9-LKR, U937 variant selected by lymphokines; U9-TR, U937 variant selected by tumor necrosis factor (TNF); WEHI-TR, WEHI-164 variant selected by TNF     

Alkylation by 1,2:5,6-dianhydrogalactitol of deoxyribonucleic acid and guanosine.

DNA was alkylated in neutral solution at 37 degrees C with 1,2:5,6-dianhydrogalactitol and hydrolysed to yield two principal products, identified as 7-galactitylguanine and 1,6-dideoxy-1,6-di(guanin-7-yl)galactitol. The reaction products were separated by chromatography on Sephadex G-10 and Dowex 50 (H+ form). The two compounds were also obtained by reaction between dianhydrogalactitol and guanosine in acetic acid. The products were characterized from their u.v.-spectral data by comparison with those of the 7-alkylguanines and were also identified by mass spectrometry.     

Chemical cross-linking of hemoglobin H. A possible approach to introduce cooperativity and modification of its oxygen transport properties.

Native and reconstituted hemoglobin H molecules were cross-linked with glutaraldehyde at pH values close to the physiological. The Schiff base adducts were analysed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis before and after reduction with sodium borohydride. The major component had a molecular weight of about 31 000 which corresponded to the dimeric species of the beta subunit. In contrast to the native protein, which has very high oxygen affinity and no heme-heme interaction or 2,3-diphosphoglyceric acid effect, the modified hemoglobin H molecules showed cooperative oxygen binding, decreased oxygen affinity and a noticeable 2,3-diphosphoglyceric acid effect.     

Stereoselective hydrogenation of methyl dideoxy- and trideoxy-β-D-hex-5-enopyranosides

Hydrogenation, severally, of methyl 3-azido-2,3,6-trideoxy-β-D-erythro-hex-5-enopyranoside, its 3-benzamido analogue, and methyl 2,6-dideoxy-β-D-threo-hex-5-enopyranoside in the presence of palladium-on-barium sulphate gave the corresponding 6-deoxy-β-D-hexopyranoside derivatives. Stereoselective addition of hydrogen was observed in each case. Methyl 2,6-dideoxy-β-D-arabino-hexopyranoside was also prepared by reductive dehalogenation of methyl 3,4-di-O-benzoyl-6-bromo-2,6-dideoxy-β-D-arabino-hexopyranoside.