Showing papers by "University of Basel published in 1980"

Lipid conformation in model membranes and biological membranes.

Abstract: Protein molecules in solution or in protein crystals are characterized by rather well-defined structures in which α-helical regions, β-pleated sheets, etc., are the key features. Likewise, the double helix of nucleic acids has almost become the trademark of molecular biology as such. By contrast, the structural analysis of lipids has progressed at a relatively slow pace. The early X-ray diffraction studies by V. Luzzati and others firmly established the fact that the lipids in biological membranes are predominantly organized in bilayer structures (Luzzati, 1968). V. Luzzati was also the first to emphasize the liquid-like conformation of the hydrocarbon chains, similar to that of a liquid paraffin, yet with the average orientation of the chains perpendicular to the lipid–water interface. This liquid–crystalline bilayer is generally observed in lipid–water systems at sufficiently high temperature and water content, as well as in intact biological membranes under physiological conditions (Luzzati & Husson, 1962; Luzzati, 1968; Tardieu, Luzzati & Reman, 1973; Engelman, 1971; Shipley, 1973). In combination with thermodynamic and other spectroscopic observations these investigations culminated in the formulation of the fluid mosaic model of biological membranes (cf. Singer, 1971). However, within the limits of this model the exact nature of lipid conformation and dynamics was immaterial, the lipids were simply pictured as circles with two squiggly lines representing the polar head group and the fatty acyl chains, respectively. No attempt was made to incorporate the well-established chemical structure into this picture. Similarly, membrane proteins were visualized as smooth rotational ellipsoids disregarding the possibility that protruding amino acid side-chains and irregularities of the backbone folding may create a rather rugged protein surface.

Folding mechanism of the triple helix in type-III collagen and type-III pN-collagen. Role of disulfide bridges and peptide bond isomerization.

Abstract: The kinetics of triple-helix formation in type III pN-collagen, type III collagen and a quarter fragment of type III collagen was followed by optical rotation and circular dichroism. Kinetic intermediates were detected by trypsin digestion and polyacrylamide gel electrophoresis. The end products of refolding at 25 degrees C were identical to the native molecules according to their melting profiles, molecular weights and sedimentation behavior. Only at low temperatures (4-15 degrees C) were mismatched structures of lower stability formed. At 25 degrees C helix formation started exclusively at the set of three disulfide bridges which link the three chains at the carboxy-terminal end. The growth of the triple helix proceeds from this single nucleus at a rather uniform rate in a zipper-like fashion. This gives rise to zero-order kinetics over a large fraction of the conversion. Consequently the time of half conversion is proportional to the length of the molecule. From the appearance and disappearance of intermediates the growth of the triple helix could be observed directly. The rate of helix propagation is determined by the rate of cis leads to trans isomerization of peptide bonds. A model mechanism was devloped which quantitatively described the overall kinetics as well as the time course of the intermediates with a single set of parameters: the rate constant of cis leads to trans isomerization k = 0.015 s-1 and an average number of 30 tripeptide units in uninterrupted stretches of residues with all peptide bonds in trans configuration.

Regulation of wound ethylene synthesis in plants

Abstract: Ethylene is produced by plants at specific stages of their life cycle and is involved in the regulation of many developmental processes, such as fruit ripening, flower fading, leaf abscission, growth in aquatic plants and initiation of flowering in bromeliads1,2. Ethylene is also formed when plants are subjected to stress by, for example, wounding, noxious chemicals, drought or waterlogging1–3. In both cases the biosynthetic pathway begins with methionine 1–5. It proceeds to ethylene by way of S-adenosylmethionine (SAM) and 1-aminocyclopropane-1-carboxylic acid (ACC), a recently discovered intermediate6,7, in ripening fruit7,8 and auxin-treated pea stem sections9,10. We now report that wound-induced ethylene synthesis also proceeds by way of ACC and that it is regulated at the level of the ACC-forming enzyme (ACC synthase). Wounding of pericarp tissue of tomato fruit (Lycopersicon esculentum Mill.) results in rapid enhancement of the activity of ACC synthase and, consequently, in a greatly increased rate of ACC synthesis.

Expression of Liver Phenotypes in Cultured Mouse Hepatoma Cells

Abstract: Mouse hepatoma cells were established in vitro as a permanently growing line designated Hepa. The mass population and a subclone were characterized for their karyotype and their retention of liver-specific properties. An examination of 17 hepatic traits revealed that the cell lines secreted several serum proteins. The activities of a number of liver-specific enzymes, however, appeared to be absent in these cells. The identification of differentiated properties of cultured hepatoma cells permits the use of these lines in a variety of studies such as cell hybridization, biochemical analysis of tissue-specific gene products, and the modulation of expression of genes governing differentiated phenotypes. This report presents the analysis of a broad spectrum of characteristics and thereby describes one of the most fully defined hepatoma cell lines of murine origin in the literature.

The yeast transposon Ty1 generates duplications of target DNA on insertion.

Abstract: Genetic elements which can transpose into different chromosomal sites causing modulation of gene expression have been found in maize1 and several other organisms2. Most intensively characterized are those in enterobacteria: the insertion sequences, short DNA segments with probably no coding information, the transposable drug-resistance genes and the phage Mu (refs 2–4). The molecular details of transpositions in bacteria are under investigation; important results are the duplication of short target sequences at the integration site.5–15. and the identification of a transposase protein16,17 . The yeast transposable element Ty1 is present in about 35 copies per genome; it is 5,600 nucleotide pairs long with terminal direct repeats of 300 nucleotide pairs and is able to integrate into new chromosomal sites18. The resemblance of this yeast element to mobile elements in Drosophila melanogaster19,20 is striking. The best characterized element, called copia, is present in about 30 copies in the Drosophila genome19,21 and can integrate into many sites22, in some cases as part of a large transposable segment23. Another remarkable structural resemblance exists with the proviral DNA of retrovirus, which can insert into different chromosomal sites, as found in avian sarcoma virus transformed rat cells24 . We focus here on the DNA sequence at the termini of element Ty1 (ref. 18). Our sequence data show that transposition in yeast and bacteria have several features in common, such as integration into different sites without any apparent sequence specificity and duplication of five nucleotide pairs of target DNA at the integration site. In addition, we find that the terminal repeats in two Ty1 elements consist of identical 338 nucleotide pairs.

Carbohydrate Changes in Glycoproteins of a Poorly Metastasizing Wheat Germ Agglutinin-resistant Melanoma Clone

Abstract: Glycoproteins of a metastasizing line of B16 mouse melanoma and a poorly metastasizing wheat germ agglutinin-resistant clone were compared. Cell surface proteins and glycoproteins were isotopically labeled by lactoperoxidase-catalyzed iodination and by NaB 3 H 4 reduction after oxidation by periodate or galactose oxidase and subsequently analyzed by gel electrophoresis and autoradiography. Differences were observed in the relative mobilities of several major cell surface components. Binding of 125 I-labeled lectins to total cellular proteins on polyacrylamide gels following electrophoresis showed that the major wheat germ agglutinin-binding components of F 1 cells were altered in Wa-4 cells. Similar differences were not observed in concanavalin A-binding components. Total cellular glycopeptides were analyzed after separation into structurally distinct classes. The acidic “complex” N -glycosidic glycopeptides from the resistant cells were of lower molecular weight than those from the parent cells. No differences were observed among the mannose-rich N -glycosidic glycopeptides or the alkali-labile O -glycosidic oligosaccharides. Structural studies involving methylation analysis revealed that in the altered glycopeptides of the resistant cells the amount of neuraminic acid residues was decreased to one-half, concomitant with an increase in the amount of fucose. The lost sialic acid was bound to C-3 of galactose, whereas the increased fucose was found on C-3 of 4-substituted N -acetylglucosamine. A possible basis for the glycosylation change and its relation to the biological behavior are discussed.

Leaky +1 and -1 frameshift mutations at the same site in a yeast mitochondrial gene.

Abstract: Two mutations in a mitochondrial structural gene, which cause leaky premature polypeptide chain termination and leaky growth, are +1 and −1 frameshifts in the same run of five T residues. The partial restoration of reading frame is probably due to ribosomal frameshifting at this site, and may be promoted by the unique structure of the yeast mitochondrial tRNAPhe (ref. 1).

Plasma norepinephrine variations with dietary sodium intake.

Abstract: Plasma catecholamine and renin activity levels were measured across a range of dietary sodium intakes (10--300 mEq/day) in 20 normal male volunteers. Supine plasma norepinephrine levels presented a triphasic pattern in relation to urine sodium, whereas epinephrine levels were not significantly altered by sodium intake, and renin showed the well-known hyperbolic relationship to urine sodium excretion. Highest supine norepinephrine values occurred at low salt intakes, the lowest when sodium excretion was between 100 and 180 mEq/day, and intermediate when sodium excretion was greater than 180 mEq/day. These findings show that sodium intake is an important consideration in the interpretation of plasma norepinephrine levels.

Fluorescence quantum yields and cascade-free lifetimes of state selected CO+2, COS+, CS+2 and N2O+ determined by photoelectron—photon coincidence spectroscopy

Abstract: The details and principles of an apparatus built for measurements of fluorescence quantum yields and cascade-free lifetimes of open-shell cations are reported. These rely on the detection of coincidences between energy selected photoelectrons and undispersed photons. The results of such measurements for CO + 2 , COS + , CS + 2 and N 2 O + in selected vibrational levels of their excited states are presented. Non-unity fluorescence quantum yields are found for some vibronic levels of CO + 2 ( B ), COS + ( A ), N 2 OP + ( A ) and a non-exponential decay is observed for CS + 2 ( A ). The data yield the following values for the radiative lifetimes: CO + 2 ( A ) 124 ± 6 ns, CO + 2 ( B ) 140 ± 7 ns, COS + ( A ) 550 ± 50 ns and N 2 O + ( A ) 240 ± 12 ns.

Biosynthesis and assembly of the proton-translocating adenosine triphosphatase complex from chloroplasts.

Abstract: The H+-translocating ATPase complex of chloroplasts consists of at least eight nonidentical subunits. Five of these (α, β, γ, δ, and e subunits) collectively constitute the globular extramembranous CF1 portion of the complex. The remaining three subunits (I-III) represent the membrane-embedded portion. Biosynthesis and assembly of these subunits were studied by pulse-labeling isolated spinach chloroplasts in the presence of cycloheximide or chloramphenicol and by translating total leaf RNA in a rabbit reticulocyte system. The labeled products were analyzed by immunoprecipitation with subunit-specific antisera or by isolating the entire H+-translocating ATPase complex in a nearly pure state. We found that chloroplasts synthesize the α, β, γ, and e subunits of CF1, the membrane-embedded subunit I, and probably also the membrane-embedded subunit III. The δ subunit (and probably also subunit II) are imported from the cytoplasm via larger precursor forms. After isolated chloroplasts are labeled in the presence of cycloheximide, the chloroplast-made H+-ATPase subunits are assembled into a complex that is indistinguishable from the authentic H+-ATPase complex. This assembly indicates that isolated chloroplasts contain excess pools of the cytoplasmically made subunits.

Identification of the Blood‐Group ABH‐Active Glycoprotein Components of Human Erythrocyte Membrane

Abstract: The blood-group ABH-active components of the erythrocyte membrane were identified by incubation of polyacrylamide gels after electrophoresis with radio-iodinated blood-group-specific lectins. The anti-A and anti-B lectin of Bandeiraea simplicifolia bound to components from A1, AB and B erythrocytes but not A2 or O erythrocytes, whereas the opposite was observed for the anti-H lectin of Lotus tetragonolobus. Both lectins revealed as major blood-group-active components band 3 and the region of band 4.5, which was resolved into at least two components. Smaller amounts of the lectins were bound to the low-molecular-weight region and the dye front, which contained the poly(glycosyl)ceramides. In addition to these components, the B. simplicifolia lectin also bound to the sialoglycoprotein bands 1 and 2 (stained with periodic acid/Schiff). The distribution of bound radioactivity, as determined with this lectin was: Band 3, 22–25%; HIO4/Schiff band-1, 10–15%; band 4.5, 34–37%; HIO4/Schiff band-2, 12–15%; and the poly(glycosyl)ceramide region, 14–17%. The different lectin-binding properties indicate a structural difference between the antigenic determinants of the sialoglycoproteins and of the other blood-group-active components. It is suggested that the antigenic determinants in the sialoglycoproteins are of the alkali-labile type previously characterized, and that the carbohydrate chains of bands 3 and 4.5 correspond to the previously isolated alkali-stable poly(glycosyl)peptides. The detection of two different groups of glycoproteins could thus explain the controversy concerning the nature of the blood-group ABH antigens in glycoproteins of the erythrocyte membrane.

Distal hamstring lengthening in cerebral palsy. An evaluation by gait analysis.

Abstract: Distal elongation of the hamstrings was performed for contracture due to neurogenic disorders in 66 patients. A follow-up study on 34 of the patients with cerebral palsy is reported here. The success of the operation was judged by functional evaluation including joint measurement and gait analysis. The advantages of this operation and the need for prolonged aftercare are discussed.

Leaf-eating invertebrates as competitors of aquatic hyphomycetes.

Abstract: Leaf-eating invertebrates selectively ingest leaf areas rich in fungal cells. The effect of this process on coincident and cumulative species diversity (species numbers and evenness) of the fungi was studied on 3 substrates (oak leaves, larch and spruce needles) in 2 hardwater and 2 softwater streams. Cumulative species number of colonizing fungi follows the equation S=k·A z(A=area below decay curve of the substrate, k=substrate-specific constant, Z=0.47). Higher feeding activity means faster weight loss of the substrate which leads to lower species richness of the fungi. The opposite is true for early successional stages on larch needles. Evenness of the fungi (distribution of individuals among species) is negatively correlated with feeding intensity by invertebrates, as measured by increased decay rates. The overall effect of leaf-eating invertebrates on aquatic hyphomycetes resembles that of potent competitors preempting substrate otherwise used by a late successional tail of relatively rare fungi.

Evidence for an Alkalilike Conduction Band in Alkali Graphite Intercalation Compounds

Abstract: The valence bands of pure graphite and several alkali graphite intercalation compounds were studied by ultraviolet photoelectron spectroscopy ($h\ensuremath{ u}=212$ eV) The most significant observation is an intensity peak at the Fermi energy ${E}_{\mathrm{F}}$ in the intercalation compounds This peak is mainly due to alkalilike $s$ states The density of states at ${E}_{\mathrm{F}}$ is enhanced by a factor of 30 compared with pure graphite The alkalilike conduction bands in the first stage alkali graphite interclation compounds are similar to those of pure alkali metals

Plasma catecholamines and cardiac, renal and peripheral vascular adrenoceptor-mediated responses in different age groups of normal and hypertensive subjects.

Abstract: The role of the sympathetic nervous system in cardiac, renal and peripheral vascular adrenoceptor-mediated responses was investigated in patients with essential hypertension and age-matched normotensive subjects. Regardless of age plasma adrenaline was significantly higher in hypertensive when compared with normotensive subjects. This suggests a sympatho-adrenal factor in essential hypertension. Plasma noradrenaline tended to increase with age but its similarity between normotensive and hypertensive subjects points to similar postganglionic neural activity and/or similar overflow of noradrenaline into the circulation. On the other hand, beta-adrenoceptor-mediated tachycardia in response to exercise and intravenous isoproterenol as well as the forearm vasodilator response to intraarterial isoproterenol decreased in normal subjects with older age. In hypertensives this age-dependent beta-receptor-related effect tends to be enhanced as judged from the greater reduction of cardiac isoproterenol sensitivity an...