Showing papers by "University of Marburg published in 1989"

Periodic-orbit quantization of chaotic systems.

Abstract: We demonstrate the utility of the periodic-orbit description of chaotic motion by computing from a few periodic orbits highly accurate estimates of a large number of quantum resonances for the classically chaotic three-disk scattering problem. The symmetry decompositions of the eigenspectra are the same for the classical and the quantum problem, and good agreement between the periodic-orbit estimates and the exact quantum poles is observed

Role of microtubules in polarized delivery of apical membrane proteins to the brush border of the intestinal epithelium.

Abstract: Colchicine- and vinblastine-induced depolymerization of microtubules (MTs) in the intestinal epithelium of rats and mice resulted in significant delivery of three apical membrane proteins (alkaline phosphatase, sucrase-isomaltase, and aminopeptidase N) to the basolateral membrane domain. In addition, typical brush borders (BBs) occurred at the basolateral cell surface, consisting of numerous microvilli that contained the four major components of the cytoskeleton of apical microvilli (actin, villin, fimbrin, and the 110-kD protein). Formation of basolateral microvilli required polymerization of actin and proceeded at glycocalyx-studded plaques that resembled the dense plaques located at the tips of apical microvilli. BBs from the basolateral membrane became internalized into BB-containing vacuoles which served as recipient organelles for newly synthesized apical membrane proteins. The BB vacuoles fused with each other and finally were inserted into the apical BB. Polarized distribution of Na+,K+-ATPase, a basolateral membrane protein, was not affected by drug-induced depolymerization of MTs. These observations indicate that Golgi-derived carrier vesicles (CVs) containing apical membrane proteins are vectorially guided to the apical cell surface by a retrograde transport along MTs. MTs are uniformly oriented towards a narrow space underneath the apical terminal web (termed subterminal space) that contains MT-organizing properties and controls polarized alignment of MTs. In contrast to apical CVs, targeting of basolateral CVs appears to be independent of MTs but demands a barrier at the apical membrane domain that prevents basolateral CVs from apical fusion (transport barrier hypothesis).

Basic fibroblast growth factor and nerve growth factor administered in gel foam rescue medial septal neurons after fimbria fornix transection.

Abstract: Basic fibroblast growth factor (bFGF) recently has been established as a survival- and transmitter-promoting neurotrophic agent for embryonic neurons in vitro. Its local application to lesioned adult optic and sciatic nerves has been shown to rescue axotomized retinal and sensory neurons that otherwise die. Following transection of the fimbria fornix pathway connecting the medial septum (MS) to the hippocampus, MS neurons undergo severe cell death, which can be prevented partially by infusion of nerve growth factor (NGF). In the same lesion paradigm, we find that 87% of these neurons visualized by cresyl-violet staining have disappeared by 4 weeks after unilateral fimbria fornix transection in adult rats. Implantation of gel foam soaked with 8 micrograms bFGF reduced neuron death to 68%. A similar rescue effect was seen with 0.3 microgram NGF. NGF administered at 20 micrograms reduced cell losses to 54%. Thus, bFGF rescued 22% and NGF at 20 micrograms 38% of the neurons that otherwise would have died. Choline acetyltransferase immunocytochemistry revealed dramatic losses of cholinergic neurons on the lesioned, compared with the unlesioned, side. Cholinergic neuron death was clearly reduced by the bFGF and NGF treatments. Basic FGF, in contrast to NGF, did not prevent a reduction in size of surviving neuronal cell bodies. Considered in the context of FGF being present in brain and hippocampal neurons, our results suggest a possible role for FGF as a neurotrophic factor for CNS neurons in vivo.

Biochemistry of acetate catabolism in anaerobic chemotrophic bacteria.

Abstract: Oxydation de l'acetate par le cycle de l'acide citrique, et par la voie a la carbone monoxide dehydrogenase, dismutation de l'acetate en dioxyde de carbone et methane chez les bacteries chimiotrophes anaerobies

Photoperiod and thermoregulation in vertebrates: body temperature rhythms and thermogenic acclimation.

Abstract: Evidence has recently begun to accumulate that photoperiodic responses of mam mals and birds may affect the control of energy balance and thermoregulation. Exposure to short photoperiod can lower the set point for body temperature regulation in birds and mam mals, as well as the voluntarily selected body temperature in ectothermic lizards. This de crease is accompanied by a reorganization of circadian or ultradian rhythms of body temper ature, particularly an increase in periods spent at rest with minimum body temperatures. Short photoperiod is also used as an environmental cue for induction of seasonal torpor or facilita tion of hibernation. During winter, cold tolerance of small mammals is improved by an in crease of nonshivering thermogenesis in brown fat. Thermogenic capacity of brown fat (res piratory enzymes, mitochondria, uncoupling protein) is enhanced in response to short pho toperiod. This response is mediated via an increase in the activity of sympathetic innervation in brown fat. Moreover, an ...

Asymmetrical recognition of the palindromic AP1 binding site (TRE) by Fos protein complexes.

Abstract: Fos and Jun proteins form a tight complex which binds specifically to the AP1 recognition sequence, a palindromic DNA element also referred to as the TPA responsive element (TRE). To elucidate the mechanism of Fos-Jun interaction with the TRE we have performed UV cross-linking studies using oligonucleotides where thymines were replaced with bromouracil. Our results indicate that both Fos and Jun directly contact the TRE but that the interaction of Fos and Jun with thymines in structurally equivalent positions in the two half sites of the TRE is different. In addition, we have carried out a comprehensive mutagenesis study of the TRE by introducing all possible point mutations plus thymine----uracil substitutions into the palindromic TRE core sequences and the adjacent nucleotides on both sides. The results of this analysis clearly show that the palindromic TRE is asymmetrical with respect to binding of Fos-Jun. We also show that a Fos protein complex with a homodimeric DNA binding site binds considerably less efficiently to TRE mutants with a perfect dyad symmetry compared with the binding to the wild-type TRE. This demonstrates that the asymmetrical recognition of the TRE is not due to the heterodimeric nature of the Fos/Jun complex but directly related to an asymmetry in the TRE sequence. The methyl groups of all four thymine residues within the TRE seem to be functionally crucial since thymine----uracil substitutions strongly reduce or abolish binding to Fos/Jun. The relevance of structurally equivalent methyl groups in the TRE core sequence is different, lending further support to the conclusion that the TRE is asymmetrical.

Coenzyme F430 as a possible catalyst for the reductive dehalogenation of chlorinated C1 hydrocarbons in methanogenic bacteria.

Abstract: Corrinoids, such as aquocobalamin, methylcobalamin, and (cyanoaquo)cobinamide, catalyze the reductive dehalogenation of CCl4 with titanium(III) citrate as the electron donor [Krone et al. (1989) Biochemistry 28, 4908-4914]. We report here that this reaction is also effectively mediated by the nickel-containing porphinoid, coenzyme F430, found in methanogenic bacteria. Chloroform, methylene chloride, methyl chloride, and methane were detected as intermediates and products. Ethane was formed in trace amounts, and several as yet unidentified nonvolatile compounds were also generated. The rate of dehalogenation decreased in the series of CCl4, CHCl3, and CH2Cl2. With coenzyme F430 as the catalyst, the reduction of CH3Cl to CH4 proceeded more than 50 times faster than with aquocobalamin. Cell suspensions of Methanosarcina barkeri were found to catalyze the reductive dehalogenation of CCl4 with CO as the electron donor (E'0 = -0.524 V). Methylene chloride was the main end product. The kinetics of CHCl3 and CH2Cl2 formation from CCl4 were similar to those with coenzyme F430 or aquocobalamin as catalysts and titanium(III) citrate as the reductant.

Macrophage activation by granulocyte/macrophage colony-stimulating factor. Priming for enhanced release of tumor necrosis factor-alpha and prostaglandin E2.

Abstract: The macrophage-activating properties of murine recombinant granulocyte-macrophage (GM)-CSF were studied in murine peritoneal macrophages with respect to metabolism, endocytosis, PGE2 and TNF-alpha release, and tumor cytotoxicity. GM-CSF was found to be a potent stimulus for RNA and protein synthesis, glucose consumption, pinocytosis, and FcR-independent phagocytosis. Macrophages were activated by GM-CSF to kill TNF-alpha-insensitive Eb lymphoma cells but failed to generate cytotoxicity against TNF-alpha-sensitive L929 cells. Although GM-CSF alone was incapable of stimulating TNF-alpha release, it primed macrophages for elevated TNF-alpha production in response to IFN-gamma plus LPS. The priming effect of GM-CSF disappeared upon longer incubation (greater than 12 h) and was followed by a strongly reduced responsiveness to stimuli that release TNF-alpha. Late-stage suppression could be reverted by treatment with the cyclooxygenase blocker indomethacin, and GM-CSF-induced priming for enhanced TNF-alpha release was entirely restored. The responsible arachidonic acid product mediating suppression was found to be PGE2, because 1) GM-CSF-primed macrophages released enhanced amounts of PGE2 and 2) indomethacin-restored macrophages were again suppressed when exogenous PGE2 was added back in amounts produced by GM-CSF-primed macrophages. Although GM-CSF potently induced TNF-alpha gene transcription by 20 h of treatment, PGE2 interfered with translation into the secreted TNF-alpha protein. These data show that GM-CSF is capable of priming for the enhanced release of two factors, initially for TNF-alpha and subsequently for PGE2. The temporally delayed generation of these two mediators suggests an autoregulatory circuit in which the later produced PGE2 limits GM-CSF-induced macrophage activation.

Nucleolar organizer regions (NORs). Basic concepts and practical application in tumor pathology.

Abstract: Summary The purpose of this investigation is to give an introduction to a novel method in tumor pathology, namely the Ag-NOR technique. The basis of this method is the argyrophilic staining of intranucleolar, non-histon proteins which are specifically associated with transcriptionally active sites of ribosomal DNA. They can therefore be considered as a marker for the protein synthesis and thus the proliferation rate of a given cell. The morphologic basis ofthe argyrophilic reaction is presented by metaphasic and interphasic tissue culture cells. The applicability of Ag-NOR technique to tumor pathology is exemplified by main results of three studies dealing with tissue sections of 65 meningiomas, whole organ sections of 50 renal carcinomas, and cytospin preparations of 30 urinary washout specimens. These studies document the considerable value of the Ag-NOR content for both, malignancy diagnosis and tumor grading. With the help of image analysis it can be shown that besides the mean number of Ag-NORs the mean area per Ag-NOR dot is of diagnostic significance. In conclusion the Ag-NOR technique is a simple inexpensive and accurate method which can be applied both to formalin fixed, paraffin-embedded tissue and cytologic specimens. As a marker of malignancy it is an invaluable new tool for the diagnostic pathologist.

A SANS Study of High Pressure Phase Transitions in Model Biomembranes

Abstract: The phase behaviour and thermotropic and barotropic phase transitions of different model biomembranes (DPPC, DMPC, DEPC and POPC*)), which consist of different hydrocarbon chain length and degree of unsaturation, have been investigated by small-angle neutron scattering (SANS) as a function of temperature and pressure up to about 65°C and 3 kbar, respectively. A pressure induced structural phase transition from a liquid-crystalline to a gel state is observed for the whole temperature range studied. The pressure of this transition increases with increasing temperature with a slope dTm/dP of about 21°C/kbar, which is common for all the different lipids investigated. The SANS experiments indicate that the effect of the two trans double bonds in DEPC and the cis double bond in the sn-2 hydrocarbon chain of POPC enhances the conformational disorder in the hydrocarbon chains not only in the liquid-crystalline, but also in the gel state. For DEPC and POPC the prefered structural conformation in the gel state is probably not tilted as it is in the gel state of the saturated phospholipids DMPC and DPPC. Only for DPPC multilamellar vesicles, an additional gel phase at higher pressures has been observed, which can be ascribed to an interdigitation of the hydrocarbon chains of opposing chains in the lipid bilayer system.

Differential distribution of apolipoprotein E isoforms in human plasma lipoproteins.

Abstract: The polymorphism of apolipoprotein E (apo E) accounts for a substantial amount of the genetic variance of cholesterol levels in man. The epsilon-2 allele and the epsilon-4 allele raises plasma and low density lipoprotein cholesterol levels as compared to the epsilon-3 allele. Whereas the lower cholesterol levels in carriers of the epsilon-2 allele can, at least in part, be attributed to the grossly deficient binding of apo E-2 to the apo B,E receptor, apo E-3 and E-4 bind to the same degree. We used gel filtration and ultracentrifugation to separate lipoproteins and subsequent immunoblotting analysis to study the apo E isoform distribution. We always found lipoproteins of lower density relatively enriched in apo E-4 and high density lipoproteins relatively depleted of apo E-4 as compared to apo E-3. This was also seen in plasma of heterozygous subjects that simultaneously express two apo E isoforms. Also, the apo E-A-II complex was directly shown by immunoblotting. Furthermore, when purified iodinated apo E was incubated with plasma in vitro, apo E-4 also reassociated more with lipoproteins of lower density than apo E-3. We conclude that apo E-3 and apo E-4 have a different lipoprotein particle distribution in vivo. This differential lipoprotein distribution may account for differences in the metabolism between apo E-3 and E-4.

Diffusion and drift of charge carriers in a random potential: deviation from Einstein's law

Abstract: Employing Monte Carlo techniques, the diffusion and drift of charge carriers within an array of hopping states subject to a Gaussian distribution of site energies of width \ensuremath{\sigma} has been studied as a function of \ensuremath{\sigma}/kT and electric field. With increasing disorder and field, significant deviations from Einstein's law are noted. They are shown to be the consequence of anomalous, field-assisted diffusion while the mobility remains constant. The effect can account for anomalous transit-time dispersion observed in polymeric photoconductors exhibiting time independent transport.

Intermittency in the coherence collapse of a semiconductor laser with external feedback.

Abstract: We report the first experimental observation of type-II intermittency in an optical system. The type-II intermittency is observed in the light intensity of a GaAs/GaAlAs semiconductor laser with external feedback in the regime of the coherence collapse. We conclude the occurrence of a time-inverted type-II intermittency from the time distribution of the observed intensity breakdowns, with the injection current as control parameter. This interpretation is confirmed by a reconstructed Poincar\'e plot exhibiting the spiraling behavior of the type-II intermittency.

Transvaginal hysterosalpingo-contrast-sonography (Hy-Co-Sy) compared with conventional tubal diagnostics

Abstract: Transvaginal hysterosalpingo-contrast-sonography (Hy-Co-Sy) is described as a new method for direct imaging of the tubal passage in tubal diagnostics. During one period of anaesthesia, a transvaginal Hy-Co-Sy was followed by either hysterosalpingography or chromolaparoscopy in 42 patients with sterility disorders. The contrast-enhanced sonography of the tubes was performed in eight cases with sterile saline solution (group 1) and 34 cases with a specially developed ultrasound contrast medium (SH U 454, group 2). The findings obtained by transvaginal Hy-Co-Sy were compared with those of the conventional method. By both methods, there was complete agreement with respect to the same evaluation of tubal passage for both sides, partial agreement when firstly the tubes were assessed as unilaterally or bilaterally open--without precise localization of the side--depending on the appearance of fluid in the pouch of Douglas, or secondly, only one side, when compared, showed agreement. In group 1 complete agreement was found once, partial agreement five times and non-agreement twice, while in group 2 complete agreement was found 22 times (65%), partial agreement 11 times and non-agreement once.

A new model to explain the redundant-signals effect.

Abstract: Le but de cet article est de proposer un modele stochastique a meme d'expliquer entierement l'effet des signaux redondants (redundant-signals effect). Ce modele qui est plus general que ceux presentes jusqu'alors est illustre avec les donnees de Miller (1986) sur le SOA (Stimulus Onset Asynchrony)

η1-C6H5CH2Li•THF•TMEDA, Kristallstruktur eines Benzyllithium•THF•TMEDA-Komplexes mit einem pyramidalen Benzyl-C-Atom

Abstract: Nach der Rontgenstrukturanalyse von [C6H5CH2Li · N(CH2CH2)3N]∞ durch Patterman, Karle und Stucky37 sowie der von [C6H5CH2Li·OEt2]∞; durch Beno, Hope, Olmstead und Power42 prasentieren wir eine weitere Benzyllithium-Strukturuntersuchung, namlich die von η1-C6H5CH2Li · THF · TMEDA (1). Im Gegensatz zu den fruheren liegt bei 1 eine monomere Benzyllithium-Verbindung vor. Auserdem ist Lithium lediglich an das benzylische C-Atom koordiniert, dessen pyramidale Konfiguration erstmals ermittelt werden Konnte. Die Molekulargewichtsbestimmung von C6H5CH2Li in THF, die ein Monomer ergab 61, und Kernresonanzuntersuchungen in THF, die auf ein pyramidales, benzylisches C-Atom bei 1 (und C6H5CH2Li53,54) hinweisen, entsprechen der Festkorperstruktur von 1. Die in den drei Festkorperstrukturen beobachteten verschiedenen Koordinationen des Lithium-Kations an das Benzyl-Anion sind wie die pyramidale Konfiguration des benzylischen C-Atoms in 1 mit quantenmechanischen Rechnungen (auch anderer Autoren45–50) in Einklang. Die pyramidale Konfiguration des benzylischen C-Atoms in 1 last vermuten, das ahnliche stereochemische Verhaltnisse zur hohen Retention beitragen, die bei der Haller-Bauer-Spaltung optisch aktiver Benzylphenylketone beobachtet wird62e–g. η1-C6H5CH2Li · THF · TMEDA, Complex with a Pyramidal Benzylic C Atom In addition to the X-ray structure determination of C6H5CH2Li · N(CH2CH2)3N]∞ by Patterman, Karle, and Stucky37 and that of [C6H5CH2Li ·OEt2]∞; by Beno, Hope, Olmstead, and Power42 we present yet another benzyllithium structure: η1-C6H5CH2Li · THF · TMEDA (1). In contrast to the earlier ones, a monomer is observed in the case of 1. Furthermore, in 1 lithium is only coordinated to the benzylic carbon atom whose pyramidal configuration has been determined for the first time. The molecular-weight determination of C6H5CH2Li in THF giving a monomer61, and NMR investigations in THF indicating a pyramidal benzylic C atom in 1 (and C6H5CH2Li53,54) correspond to the solid-state structure of 1. The different coordinations of lithium observed in the three solid-state structures and the pyramidal configuration of the benzylic C atom in 1 are in agreement with theoretical studies (also of other authors45–50). The pyramidal configuration of the benzylic C atom of 1 suggests that a similar stereochemical situation contributes to the high retention observed recently in Haller-Bauer cleavage reactions of optically active benzylic ketones62e–g.

Function of methanofuran, tetrahydromethanopterin, and coenzyme F420 in Archaeoglobus fulgidus

Abstract: Archaeoglobus fulgidus is an extremely thermophilic archaebacterium that can grow at the expense of lactate oxidation with sulfate to CO2 and H2S. The organism contains coenzyme F420, tetrahydromethanopterin, and methanofuran which are coenzymes previously thought to be unique for methanogenic bacteria. We report here that the bacterium contains methylenetetrahydromethanopterin: F420 oxidoreductase (20 U/mg), methenyltetrahydromethanopterin cyclohydrolase (0.9 U/mg), formyltetrahydromethanopterin: methanofuran formyltransferase (4.4 U/mg), and formylmethanofuran: benzyl viologen oxidoreductase (35 mU/mg). Besides these enzymes carbon monoxide: methyl viologen oxidoreductase (5 U/mg), pyruvate: methyl viologen oxidoreductase (0.7 U/mg), and membranebound lactate: dimethylnaphthoquinone oxidoreductase (0.1 U/mg) were found. 2-Oxoglutarate dehydrogenase, which is a key enzyme of the citric acid cycle, was not detectable. From the enzyme outfit it is concluded that in A. fulgidus lactate is oxidized to CO2 via a modified acetyl-CoA/carbon monoxide dehydrogenase pathway involving C1-intermediates otherwise only used by methanogenic bacteria.

Stereoselective synthesis of alcohols, XXXI: Stereoselective CC bond formation using chiral Z‐pentenylboronates

Abstract: Using 1,2-dicyclohexyl-1,2-ethanediol as chiral auxiliary, the enatiomerically pure Z-pentenylboronate 9c was obtained. Its addition to benzaldehyde proceeded with complete transfer of chirality to give the syn-E-homoallyl alcohol 11. The ability of the reagent 9c to create new stereocenters under reagent control of diastereoselectivity was tested in its addition to the chiral aldehydes 15 and 24. This resulted in a short and stereospecific synthesis of invictolide (18), as well as of a C-9/C-15-partial structure 25 of erythronolide A. Stereoselektive Synthese von Alkoholen, XXXI. — Stereoselektive C-C-Bindungsbildung mit Hilfe chiraler Z-Pentenylboronsaureester Unter Verwendung von 1,2-Dicyclohexyl-1,2-ethandiol als chiralem Auxiliar wurde der enantiomerenreine Z-Pentenylboronsaureester 9c erhalten. Dessen Addition an Benzaldehyd ergab den syn-E-Homoallylalkohol 11 unter vollstandiger Chiralitats-Ubertragung. Die Fahigkeit des Reagenz 9c zur Bildung neuer Stereozentren unter Reagenz-Kontrolle der Diastereoselektivitat wurde in der Addition an die chiralen Aldehyde 15 und 24 gepruft. Dies fuhrte zu einer kurzen stereospezifischen Synthese des Invictolids (18) wie der eines C-9/C-15-Bausteins 25 des Erythronolids A.