Showing papers by "University of Konstanz published in 1970"

Ion flux across lipid bilayer membranes with charged surfaces.

Abstract: In this paper we derive expressions for the ion flux across lipid bilayer membranes with charged surfaces treating the membrane as a continuous phase interposed between two electrolyte solutions and calculating the ion flux with the Nernst-Planck equations. The theoretical results are compared with experiments of Seufert and Hashimoto on lipid bilayer membranes with charged surface active agents added to the membranes. If the charge of both membrane surfaces has the same sign the flux of the gegenions is greatly increased whereas the flux of the coions decreases to a small amount. For oppositely charged membrane surfaces the membrane behaves like a np semiconductor and typical rectification voltage-current characteristics are obtained.

Zentrale versus periphere Kontrolle des Gesanges von Grillen (Gryllus campestris)

Abstract: Bei Gryllus campestris werden Singbewegung und Aktivitat einiger mesothorakaler Singmuskeln untersucht. Aus operativen Eingriffen in das Bewegungssystem, die Muskeln und ihre Nerven sowie in die Konnektive des thorakalen Bauchmarks wird gefolgert: Die Gesange der Grillen sind uberwiegend zentral programmiert; eine periphere Kontrolle verandert sie nur in engen Grenzen. Lautmuster und zugeordnete Muskelaktivitat werden kaum geandert, nachdem die Tegmina oder die Mittelbeine einseitig oder beidseitig amputiert sind, ebenso wenig nach Belasten der Vorderflugel mit Gewichten bis zu 120 mg. Grillen mit kurzen Vorderflugeln „forme neotenique“ und mit langen Hinterflugeln „forme makroptere“ zeigen ebenfalls ein normales Aktivitatsmuster der Muskeln. Tegmina, die in der Ruhelage festgelegt sind, beeinflussen lediglich die Entladungshaufigkeit der „fast“-Einheiten im Subalar- und 2. Basalarmuskel, und zwar links mehr als rechts. Es wird nach solchen Eingriffen eine Asymmetrie im motorischen System der Grillen aufgedeckt. Auch eine Belastung der Tegmina, nicht aber die Amputation, erhoht die Muskelaktivitat, allerdings nur in Pleuralmuskeln der linken Seite. Muskeln, deren ventrale Ansatzstellen am Sekelet durchtrennt sind, degenerieren nicht, solange Sauerstoffversorgung und Innervation gewahrleistet sind. Im Gesang, der auch noch nach solchen Eingriffen auftritt, arbeiten sie wie beim normalen Tier. Grillen konnen noch zirpen, wenn die Pro- und Remotoren und die Subalar- und Basalarmuskeln an einer Ansatzstelle abgelost sind; ja selbst nach Denervierung dieser Muskeln kann man von den Einheiten der intakt gebliebenen dorsalen Langsmuskeln die gesangsspezifische Aktivitat ableiten. Nur nach der Durchtrennung des linken Konnektivs zwischen dem 1. und 2. Brustganglion findet man eine Assymmetrie in der Muskelaktivitat, wobei nur die linke Seite betroffen ist. Dabei konnen Subalar- und 2. Basalarmuskel ihre Entladung erhohen, ggf. tonisch feuern.

Space charge-limited conductance in lipid bilayer membranes.

Abstract: A mathematical treatment is given for the flux of ions of one charge sign across lipid bilayer membranes This treatment is a generalization of a previous analysis of the membrane conductance by D Walz, E Bamberg and P Lauger which was restricted to systems with negligible space charge in the membrane The present theory includes space charge effects, and it is no longer assumed that the electric field strength in the membrane is constant It is found that the ohmic membrane conductivity λ0 is reduced by space charges; if only ions of one charge sign are soluble in the membrane, λ0 approaches a limiting value for increasing concentration of the permeable ion in the aqueous solution The theory also predicts the range in which the constant field approximation is valid It is found that space charge effects become predominant when the mean concentration of the permeable ion in the membrane exceeds 5×10−5 m The currentvoltage characteristic of the membrane remains practically linear even in the presence of a high space charge It is therefore concluded that the experimentally observed nonlinearity is caused mainly by the distortion of the potential energy profile of an ion due to image forces

k-Band-Simulation von k-Kopf-Turing-Maschinen

Abstract: Es werdenTuring-Maschinen mitk unabhangigen Lese-Schreib-Kopfen auf einem Band undTuring-Maschinen mit je einem Kopf aufk Bandern betrachtet. Es wird gezeigt, das sich ohne Verandern der Rechenzeit jede Maschine von einem Typ durch eine Maschine vom andern Typ simulieren last. Daraus wird gefolgert, das es fur die Rechengeschwindigkeit vonTuring-Maschinen nur auf die Zahl der Kopfe, nicht aber auf deren Verteilung auf einzelne Bander ankommt.

The synthesis of succinate-dehydrogenase riboflavin

Abstract: Singer and Kearney"], in their early studies, recognized that the flavocoenzyme of mitochondria1 succinate dehydrogenase ("SD-flavin") [**I was a derivative of flavin-adenine-dinucleotide which was covalently bound to the protein. In cooperation with Dr. Singer's team [***I, we have attempted to elucidate the structure of this coenzyme. In the first preliminary communication I21, we concluded from the hyperfine structure of electron spin resonance (ESR) spectra of partially purified SD-riboflavin (obtained from SD-FADpeptide mixtures by total hydrolysis in 6 N HCl) that

Blocking phenomena and charge transport through membranes

Abstract: Substances which uncouple oxidative phosphorylation in mitochondrial membranes usually increase the electrical conductivity of synthetic bimolecular phospholipid membranes. Among these uncouplers is a group characterized chemically as weak acids. For this group the conductivity of synthetic membranes, when measured versus pH at fixed uncoupler concentration, shows a maximum at a pH approximately equal to the pK value of the uncoupler used. Corresponding maxima in membrane electrical potential arising from ion concentration gradients are also observed. To explain such phenomena a model is proposed which assumes charge transport by the direct transfer of either protons or anions of the uncoupler between binding sites located on the membrane boundaries. A fixed surface density of such sites is assumed. The transfer of an ion requires both its presence on an initiating site and the availability of a terminal site which is not already occupied by an ion of the same species. Failure to satisfy both criteria leads to blockage of current flow at both low and high concentrations of the transported ion.

Zur Stabilität und Struktur der CuI‐Komplexe des Imidazols und Histamins. Chemie des einwertigen Kupfers in homogener, polarer Lösung. 1. Mitteilung

Abstract: Univalent copper is stabilized in aqueous medium by the non-protophilic ligand CH3CN, allowing ligand displacement reactions to be investigated as if a stable CuI-hydrate did exist. Under these conditions the formation of CuI-complexes with imidazole and its derivatives has been studied in polar solution in the absence of CuII. Imidazole (ImH) acts upon CuI as a bidentate ligand forming polynuclear chains according to the equation Histamine reacts in the same way, i. e. the coordination number of CuI does not exceed 2; by comparison of the complexes of CuI with histamine and its N-methyl-derivatives it is shown that no six-membered chelate – which sterically would be possible – is built up. Trigonal as well as tetrahedral coordination of CuI – i. e. chelate formation – in dilute polar solutions are confined to π- or d-acceptor ligands, e. g. bipyridine or methionine. Conclusions are drawn from this on the requirements for redox-active copper in proteins.

Pteridines, XXXVIII. Synthese und Eigenschaften von 2.4-Diamino-6- und -7-oxo-dihydropteridinen

Abstract: Verschieden substituierte 2.4-Diamino-7- und -6-oxo-dihydropteridine (7–10 bzw. 12 –14) werden aus Tetraaminopyrimidinen (1–4) dargestellt und die Strukturen anhand von pK-Werten und UV-Spektren diskutiert. Pteridines, XXXVIII. Synthesis and Properties of 2,4-Diamino-6- and -7-oxodihydropteridines Various substituted 2,4-diamino-7- and -6-oxodihydropteridines (7–10 and 12–14, respectively) have been prepared from tetraaminopyrimidines (1–4). Their structures are discussed on the basis of pK-values and u.v. spectra.

Quaternary Structure and Enzymic Properties of Beef Liver Glutamate Dehydrogenase

Abstract: The molecular weight of NAD-dependent dehydrogenases varies from some twenty thousands to some millions. Most of the molecular weights are in the range 50, 000 to 200, 000 (1). The subunit structure of the majority of dehydrogenases is now well established, most of them are composed of more than one polypeptide chain. All these enzymes consist of polypeptide chains with molecular weights between 14, 000 and 50, 000 (1, 2). In general only the associated molecule is observed in the native state. If this is the case it can be assumed that the self-assembly process to the associated and active molecule leads to such an important lowering of free energy that in the native state the equilibrium concentration of the single polypeptide chain is far below detectibility.

Die verteilung der Propriorezeptoren im spinnenbein

Abstract: Every joint of the walking legs and the pedipalps of the tarantula is equipped with at least 2 groups of proprioceptors There is a total of 18 groups containing around 135 neurones They lie at the most “strategic” points, ie right at the pivots, where stress and strain are maximal during movements The greatest number, namely 5 groups, is to be found at the coxotrochanteral joint, a ball and socket joint that permits movements in nearly every plane At least some of the receptor cells are multipolar

Electrical characteristics of the ionic psn-junction as a model of the resting axon membrane.

Abstract: As a model for the resting axon membrane, we propose the ionic psn-junction. Its electrical characteristics can be determined in close analogy to the corresponding electronic semiconductor junction. Using the “semianalytic approximation”, we calculated the electrical capacity and the ionic currents. In contrast to the abrupt pn-junction, the electrical capacity of the psn-junction turns out to be practically voltage-independent, as it is observed for the squid axon membrane. The passive ionic fluxes for K+, Na+ and Cl−, as the main contributions to the total charge flux, are calculated and compared with literature data on the ion fluxes through the resting squid axon membrane as measured by use of radioactive tracers. From this comparison, the ionic permeabilities can be evaluated and used to compute the resting membrane conductivity, which is found to be close to the experimental value. Further evidence in favor of the proposed asymmetrical membrane structure and possible ways of its test by the methods of protein chemistry are discussed.

Künstliche Lipidfilme als Modelle biologischer Membranen

Abstract: This article gives a short review of recent experiments with artificial lipid membranes in aqueous phase. These films have a thickness of about 70 ~t and consist of a double layer of oriented lipid molecules; they are valuable models for the study of certain phenomena in biological membranes, such as the mechanism of carriermediated ion transport. Interesting nonlinear electrical phenomena have also been observed with these membranes.

Electronmicroscopic studies on the foraminifer Allogromia laticollaris Arnold

Abstract: Das Cytoplasma der Agamonten von Allogromia laticollaris ist durch zahlreiche Vakuolen bzw. Lakunen charakterisiert, deren Ausdehnung vom Alter der Zellen abhangt. Bei wachsenden Agamonten ist das Cytoplasma relativ dicht, und die meisten Kerne zeichnen sich durch eine Vesikelzone an der Kernhulle aus. In spateren Entwicklungsstadien treten in zunehmendem Mase auch Kerne auf, die stattdessen von einem Vakuolensystem umgeben sind. Das an den Kern angrenzende Cytoplasma ist stark zerkluftet. Man kann in bezug auf die strukturelle Differenzierung des kernnahen Cytoplasmas zwei Zustandsformen ein und desselben Kernes unterscheiden, wobei die Indentitat durch Ubergangsstadien gesichert ist.

Ein funktionentheoretischer beweis des satzes von Müntz

Abstract: Muntz's theorem for the intervall [0,∞] as shown by Crum in [3] is generalized by using exponential polynomials instead of exponential sums as approximating functions. A relationship to the Paley-Wiener-class of the right half-plane is also shown. By modifying the proof of this theorem, Muntz's theorem is then proved for the bounded interval [-α,α]. Analogously a relationship is obtained to the Paley-Wiener-class of the degree α.

Enzymaktivitäten der menschlichen Leber bei Hyperthyreose und Hypothyreose

Abstract: In thyrotoxicosis the activity of PGM was decreased, the activities of GAPDH, PEP-CK, ME and CAT were increased and the activity of GP-OX was unchanged.

Wirtschaftswachstum und die verwendung des arbeitspotentials

Abstract: SUMMARY The present article deals systematically with the objections against the traditional manpower-approach. The result thereof is a catalogue of variably urgent research aims. The wide-spread pessimism concerning the possibilities of methodically extending the manpower-approach thereby turns out to be at least premature. The traditional manpower-approach is very inflexible. It is based on the assumption of a predetermined expansion of final demand and labour productivity and takes coefficients as fixed. This means among other things that political decisions —like determining the teacher/pupil-ratio or the share of research workers among total personnel—cannot be changed. In the article is outlined how to overcome these shortcomings. Allowing for decision margins in dividing up the labour force between the production of consumption- and capital-goods and between education and research poses difficult theoretical and statistical problems; but it does not fundamentally make impossible the application of the manpower-approach.

Myth, collective trauma and war in Serbia: a cultural-hermeneutical appraisal

Abstract: This paper explores the close relationship between mythical narrative, collective trauma and their repercussions on the Serbian population since the mid-1980s. It is argued that Serbia's particular cultural-historically inherited frame of perception provided a fertile seedbed for Milosevic to successfully launch a policy of re-traumatization and thus establish widespread consent to his war policy among the population. Other cultural factors that might have contributed to broad approval of Milosevic's policy will be reflected on. Drawing on recently coined concepts like 'cultural trauma' and 'cultural fear', a specifically cultural-sociological perspective on the subject will be outlined.