Showing papers by "Humboldt University of Berlin published in 1984"

Methionine sulfoxide formation: the cause of self-inactivation of reticulocyte lipoxygenase.

Abstract: Under conditions leading to inactivation of reticulocyte lipoxygenase by 13ls-hydroperoxylinoleic acid a single methionine, presumably in the active center of the enzyme, is oxidized to methionine sulfoxide.

The mechanism of inactivation of lipoxygenases by acetylenic fatty acids

Abstract: The inactivation of soybean lipoxygenase by 5,8,11,14-eicosatetraynoic acid was studied in detail. The inactivation was found to be time-dependent and irreversible. A kinetic scheme, based on the assumption of a rapid inactivation of the enzyme-product complex, yielded a Km value for 5,8,11,14-eicosatetraynoic acid of 1.3 microM, which is about a tenth of that described for arachidonic acid, and a reaction constant k+2 of 0.006s-1, which is four orders of magnitude lower. The reasons for these differences are discussed. Several types of experimental evidence indicate that the first step of the enzyme inactivation is the conversion of 5,8,11,14-eicosatetraynoic acid via a lipoxygenase reaction: (a) the conversion of radioactively labelled methyl ester of 5,8,11,14-eicosatetraynoic acid to other products; (b) the oxygen requirement of the inactivation; (c) the competitive protective effect of linoleic acid; (d) the similarity of the activation energy for both the dioxygenation of linoleic acid and the enzyme inactivation by 5,8,11,14-eicosatetraynoic acid; (e) the formation of one mole methionine sulfoxide/mole enzyme during the reaction with 5,8,11,14-eicosatetraynoic acid, similar to the suicidal reaction of reticulocyte lipoxygenase with 13LS-hydroperoxy-linoleic acid. These results, as well as the lack of covalent binding of 14C-labelled 5,8,11,14-eicosatetraynoic acid methyl ester, contradict the allene mechanism postulated by others [D.T. Downing, D.G. Ahern, and M. Bachta (1970) Biochem. Biophys. Res. Commun. 40, 218-223; K.H. Gibson (1977) Chem. Soc. Rev. 6, 489-510]. It is assumed that the susceptible methionine is located at the active centre of the enzyme.

Accounting for the ATP-consuming processes in rabbit reticulocytes

Abstract: The report deals with a detailed balance of ATP production and consumption of the rabbit reticulocyte. 1. The sum-total of ATP produced amounts to 135mmol · l−1· h−1. 2. About 70% of the ATP consumption has been accounted for by specific processes. The main contributing processes are the globin synthesis with about 28%, the Na+, K+-ATPase with 23% and the proteolysis with more than 15%. 30% of ATP consumption has not been accounted for. 3. Cycloheximide (20 μM) leads to a dissociation between synthesis and degradation of proteins, which argues against any obligatory connection between these processes. 4. More than 90% of the lysine liberated from mitochondria by proteolysis were reutilized for the globin synthesis demonstrating the high nitrogen economy of reticulocytes. 5. Each of the ATP-consuming processes studied appears to control ATP production in an independent manner without competition with each other.

Clozapine--a serotonin antagonist?

Abstract: The effect of clozapine on the central serotonergic transmission system was studied by investigation of open-field motility of rats after microinjection of drugs into nucleus accumbens and median raphe nucleus. Previous work has shown that LSD in low doses potentiates apomorphine-induced hypermotility and that this LSD effect is induced by a serotonin agonist action in median raphe nucleus. Clozapine, injected into median raphe nucleus (0.05 micrograms), suppressed the LSD effect in the same manner as serotonin antagonists did. Since alpha-adrenergic drugs, injected into median raphe nucleus, caused locomotor stimulant effects, an alpha- adrenalytic action of clozapine was excluded. Clozapine, injected into nucleus accumbens (0.2 micrograms), increased apomorphine-induced hypermotility, whereas the dopamine antagonist haloperidol suppressed it. Our results suggest a serotonin antagonist action of clozapine.

Diffusion and reaction in random media and models of evolution processes

Abstract: A diffusion equation including source terms, representing randomly distributed sources and sinks is considered. For quasilinear growth rates the eigenvalue problem is equivalent to that of the quantum mechanical motion of electrons in random fields. Correspondingly there exist localized and extended density distributions dependent on the statistics of the random field and on the dimension of the space. Besides applications in physics (nonequilibrium processes in pumped disordered solid materials) a new evolution model is discussed which considers evolution as hill climbing in a random landscape.

Resonatorless Optical Bistability Based on Increasing Nonlinear Absorption

Abstract: A new type of optical bistability is presented. Instead of a resonator the intrinsic feedback between the optical excitation of carriers and their recombination is used. Optical bistability appears, if the absorption coefficient increases with growing carrier density. Both propagation effects and carrier diffusion are considered. Analytical model calculations are carried out for an abrupt behaviour of the absorption coefficient. The results explain the hysteresis in the transmittivity of CdS, recently observed. Ein neuer Typ optischer Bistabilitat wird vorgestellt. Anstelle des Resonators wird die innere Ruckkopplung zwischen der optischen Anregung von Ladungstragern und ihrer Rekombination benutzt. Optische Bistabilitat entsteht, wenn der Absorptionskoeffizient mit zunehmender Tragerdichte wachst. Sowohl Ausbreitungseffekte als auch Tragerdiffusion werden betrachtet. Analytische Modellrechnungen werden fur einen abrupten Verlauf des Absorptionskoeffizienten durchgefuhrt. Die Ergebnisse erklaren die kurzlich experimentell beobachtete Hysterese im Transmissionsvermogen von CdS.

A metabolic osmotic model of human erythrocytes.

Abstract: A metabolic osmotic model of red blood cells is presented which takes into account the main reaction steps of glycolysis and the passive and active fluxes of ions across the cell membrane. Cellular energy metabolism and osmotic behaviour are linked by the ATP consumption for the active transport of cations as well as by the osmotic action of the glycolytic intermediate 2,3-diphosphoglycerate (2,3-DPG). The model is based on a system of differential equations describing the metabolic reactions and transport processes. Further, two algebraic conditions for the osmotic equilibrium and the electroneutrality of the cell are considered. Using realistic system parameters the model allows the calculation of a great number of dependent variables, among them the cell volume, the concentrations of metabolites and ions and the transmembrane potential. Only stationary states are considered. The parameter dependence of important model variables is characterized by control coefficients. The main results are: (a) The volume of erythrocytes is mainly determined by the permeabilities of the leak fluxes of cations, the content of hemoglobin and the activity of the hexokinase-phosphofructokinase system of glycolysis; (b) Changes of volume affect the glycolytic rate mainly by changing the concentration of ATP which is a regulator of glycolysis; (c) A change in the membrane area may affect the other cell properties only if it is connected with variations of the number of active and leak sites of the membrane.

Energy Transfer Processes in (Zn, Mn)S Mixed Crystals

Abstract: (Zn, Mn)S mixed crystals with Mn concentrations up to 32 mol% and electron-beam evaporated (Zn, Mn)S thin films are studied by photoluminescence emission, excitation, and decay measurements in the temperature range2 to 300 K. Besides the usual yellow an additional red emission band is observed with the same excitation spectrum. The measured characteristic temperature and Mn-concentration dependence of the intensities and decay times of both bands are quantitatively discussed on the basis of an effective-lifetime model assuming a radiationless resonance energy transfer from the primarily excited Mn2+ ions via several other Mn2+ ions finally to red emission and nonradiative centres, respectively. This model is further supported by the measured time dependence of the pulse-excited red emission intensity reaching its maximum only after a Mn-concentration dependent delay time. Characteristic parameters of the energy transfer between the Mn2+ ions are determined. The nature of the red emission centres is discussed, especially in connection with the occurrence of octahedrally coordinated Mn2+ ions at high Mn concentrations. (Zn, Mn)S-Mischkristalle mit Mn-Konzentrationen bis zu 32 mol% und durch Elektronenstrahl-Verdampfung hergestellte (Zn, Mn)S-Dunnschichten werden durch Emissions-, Anregungs- und Abklingmessungen der Photolumineszenz im Temperaturbereich von 2 bis 300 K untersucht. Neben der ublichen gelben wird eine zusatzliche rote Emissionsbande mit dem gleichen Anregungsspektrum beobachtet. Diegemessene charakteristische Temperatur- und Mn-Konzentrationsabhangigkeit der Intensitaten und Abklingzeiten beider Banden werden quantitativ diskutiert auf der Grundlage eines Effektivlebensdauer-Modells, das strahlungslose Resonanzenergieubertragung von den primar angeregten Mn2+-Ionen uber mehrere andere Mn2+-Ionen annimmt, die schlieslich zu den rot-emittierenden bzw. zu strahlungslosen Zentren fuhrt. Dieses Modell wird weiter unterstutzt durch die bei Impulsanregung gemessene Zeitabhangigkeit der Intensitat der roten Emissionsbande, die erst nach einer von der Mn-Konzentration abhangigen Verzogerungszeit ihr Maximum erreicht. Die charakteristischen Parameter der Energieubertragung zwischen den Mn2+-Ionen werden bestimmt. Die Natur der Zentren der roten Emission wird diskutiert, insbesondere im Zusammenhang mit dem Auftreten von oktaedrisch-koordinierten Mn2+-Ionen bei hohen Mn-Konzentrationen.

Primary central nervous system tumors in stillborns and infants. Epidemiological considerations.

Abstract: An epidemiologic investigation of true neoplasms of the central nervous system in fetuses and infants in the German Democratic Republic (GDR) was undertaken. Since all fetal deaths and all deaths in the first year of life are subject to a full postmortem examination and since all cancer cases or deaths are reported to a central registry, the prerequisites for a valid assessment of the incidence of these tumors are present. During the years 1960–1979, 55 histopathologically verified tumors of the central nervous system were identified in the GDR, a frequency of approximately 1.1 per 100 000 births. Unexpectedly, medulloblastoma (13 cases) was the most frequent tumor type.

Respiratory rhythmically regulated electrical stimulation of paralyzed laryngeal muscles

Abstract: Electrical stimulation of the posterior cricoarytenoid muscle, synchronized with inspiration, was achieved in dogs, utilizing a radio frequency stimulus triggered by a chest wall expansion transducer. This system brings about the abduction of the paralyzed vocal cord for the entire duration of inspiration, which allows a normal flow of air through the larynx. The stimulation system could be tested successfully in actual experiments in dogs with artificial paralysis of the recurrent laryngeal nerve. Its effectiveness could be proved through observation of the vocal cord movements (photographic documentation) and recording subglottic pressure variations. Transmission of stimulation energy is effected by electrical induction.

The Electron—Hole Plasma at Finite Temperatures. Calculation of Exchange-Correlation Energies and Padeé Approximants

Abstract: The thermodynamics of an electron—hole plasma is investigated with special emphasis on the temperature dependence of exchange (x) and correlation (c). The basic quantity of the RPA approach used, is the free energy as a function of density and temperature. In a wide density range a remarkable compensation is found of the temperature dependence between x and c which is exemplified for the chemical potential. Numerical results are presented with parameters modelling Ge and GaAs. For the phase diagram minor changes result compared with the usual approach taking xc at zero temperature. For practical purposes Pade approximants are constructed. Die Thermodynamik des Elektron—Loch-Plasmas wird unter Berucksichtigung der Temperaturabhangigkeit von Austausch (x) und Korrelation (c) untersucht. Ausgangspunkt der RPA-Rechnung ist die Freie Energie als Funktion von Dichte und Temperatur. In einem relativ grosen Dichtebereich findet man eine weitgehende Kompensation der Temperaturabhangigkeiten von x und c, was am Beispiel des chemischen Potentials gezeigt wird. Es werden numerische Ergebnisse fur Modellparameter von Ge und GaAs angegeben. Fur das Phasendiagramm ergeben sich nur geringe Anderungen gegenuber der ublichen T = 0-Naherung fur xc. Fur praktische Zwecke werden Pade-Formeln konstruiert.

Stimulation of wound healing, using brain extract with fibroblast growth factor (FGF) activity. III. Electron microscopy, autoradiography, and ultrastructural autoradiography of granulation tissue

Abstract: A bovine brain fraction with FGF activity (fibroblast growth factor) increased the formation of granulation tissue of rats in an experimental wound healing model. It was characterised by intensified formation of new capillaries, stimulation of the synthesis function of fibroblasts and myofibroblasts, and proliferation of freshly developed granulation tissue. The results obtained from light microscopy and autoradiographic electron microscopy with 3H-thymidine suggested significant increase in the labelling of activated, undifferentiated endothelial cells in vascular sprouts and of differentiated endothelial cells in developed capillaries. FGF S3 appeared to speed up the differentiation of freshly formed endothelial cells. Also labelled were pericytes and other fibroblastoid cells, undifferentiated mesenchymal cells, juvenile undifferentiated fibroblasts, mature fibroblasts, myofibroblasts, and macrophages. Pericytes are presumed to be preferential precursors of myofibroblasts, on account of their occurrence in time and similar ultrastructural parameters. Close neighbourhood of lymphocytes and labelled fibroblasts gave rise to the assumption of specific effects, such as stimulation by lymphokines.

Influence of surface charge and transmembrane potential on rubidium-86 efflux of human red blood cells.

Abstract: The dependence of the rate constant of Rb/sup +/ efflux on extracellular cation concentration was measured. At low ionic strengths Rb/sup +/ efflux increased strongly. Permeability coefficients were calculated from the rate constants measured, using the Goldman flux equation, with and without making allowance for surface potentials. Only when allowance was made for surface potentials and the associated differences between ion concentrations in the bulk solutions and at the membrane surface, the permeability coefficient remained constant. Best agreement between experimental data and theoretically calculated values was obtained when an interior surface potential of -110 mV was assumed. When the surface charge of erythrocytes is reduced by neuraminidase, the rate constants for Rb/sup +/ efflux decreased, indicating a significant influence of surface potential.

Estimators of the Mean Squared Error of Prediction in Linear Regression

Abstract: If a linear regression model is used for prediction, the mean squared error of prediction (MSEP) measures the performance of the model. The MSEP is a function of unknown parameters and good estimates of it are of interest. This article derives a best unbiased estimator and a minimum MSE estimator under the assumption of a normal distribution. It compares the bias and the MSE of these estimators and some others. Similar results are presented for the case in which the model is used to estimate values of the response function.

Kilovolt Electron Energy Loss Distribution in GaAsP

Abstract: Using the electron beam induced barrier current and Monte Carlo simulation the depth-dose function as well as the distribution function for the generation source for electron-hole pairs perpendicular to the injection direction are determined. The lateral dose distributions show measured and calculated a part I formed by the focused electron beam penetrating into the solid target and a part II due to the progressive spreading of the electron beam during the interaction with the target. Spatial dose distributions are computed for the typical case of scanning electron microscopy and for the electron microprobe analysis. Die Tiefendosiskurve und die Verteilung der Elektron-Loch-Paargeneration senkrecht zur Einschusrichtung werden unter Ausnutzung des elektronenstrahlinduzierten Stromes sowie mit Monte-Carlo-Rechnungen ermittelt. Die experimentell und rechnerisch erhaltenen Lateralverteilungen bestehen aus einem Teil I, der durch das Eindringen des fokussierten Elektronenstrahles in den Festkorper hervorgerufen wird und einem Teil II, der sich durch die Aufspreizung des Elektronenstrahles infolge der Wechselwirkung mit dem Festkorper ausbildet. Fur den typischen Fall der Rasterelektronenmikroskopie und der Elektronenstrahlmikroanalyse werden die raumlichen Dosisverteilungen angegeben.

On sources of error in the biochemical study of perilymph (guinea-pig).

Abstract: Contamination of perilymph with other fluids (cerebrospinal fluid, tissue fluid, blood, endolymph) together with sampling, anaesthesia, surgical intervention or food intake of the animals may considerably affect the analytical result. The numerous possible artefacts seem to be the main reason why varying values are given in the literature for the same chemical component of perilymph. This is also partly true of cerebrospinal fluid and blood. The effect of some sources of error on selected chemical components of perilymph, cerebrospinal fluid and blood is briefly summarized.

Fortschrittsbericht Zur alimentären Aufnahme, Analytik und biologischen Bedeutung des Thiocyanats†

Abstract: Es wird eine Ubersicht zur alimentaren Aufnahme, Metabolisierung und Elimination sowie zur biologischen Bedeutung des Thiocyanats (SCN−) im Saugetierorganismus gegeben. SCN− stellt einen bedeutenden Nahrungsfaktor dar, da es wichtige Korperfunktionen, z. B. die Immunantwort, beeinflust. Bei der analytischen Bestimmung in pflanzlichen und tierischen Lebensmitteln konnen die reversible Bindung des SCN− an Proteinmolekule sowie bei der Umsetzung mit Brom interferierende Naturstoffe, z. B. Aminosauren und Cyanid aus glycosidischen Vorstufen, zu erheblichen Storungen fuhren. Die Umgehung dieser Storungen gelingt durch ein kombiniertes papierchromatographisches/gaschromatographisches Verfahren. Mit Ausnahme von Brassica-Arten, bei denen relativ hohe SCN− -Mengen glucosidisch gebunden vorliegen, enthalten pflanzliche Lebensmittel etwa 0,1–1,3 mg SCN−/kg Frischmaterial, tierische Lebensmittel wie Milch und Milchprodukte 3–9 mg SCN−/1 bzw. kg, Muskelfleisch z. B. vom Rind, 0,5–0,7 mg SCN−/kg. Bilanzberechnungen ergaben, das Nichtraucher durchschnittlich 1,8–5,2 mg SCN−/d alimentar aufnehmen.

Two‐loop Renormalization of Non‐smooth String Operators in Yang‐Mills Theory

Abstract: The renormalization constants for string operators both with smooth and non-smooth non-self-intersecting open contour have been evaluated up to the order g4. 2-Loop-Renormierung nichtglatter String-Operatoren in der Yang-Mills-Theorie Es sind die Renormierungskonstanten fur String-Operatoren mit sowohl glatter als auch nichtglatter, einfacher, offener Kontur bis zur Ordnung g4 berechnet worden.

Optical Study of ZnS:Mn Thin Films with High Mn Concentrations

Abstract: Electron-beam evaporated ZnS: Mn thin films with high Mn concentrations between 2 and 6 mol% are studied by photoluminescence emission, excitation, and decay measurements in the temperature range 28 to 300 K. The usual yellow and an additional red emission band with the same excitation spectrum are found similarly to the results for highly Mn-doped ZnS single crystals. The observed characteristic temperature and Mn-concentration dependence of both bands are quantitatively discussed on the basis of an effective-lifetime model assuming a radiationless resonance energy transfer from the primarily excited Mn2+ ions via several other Mn2+ ions by an exchange mechanism finally to red emission and nonradiative centres, respectively. Especially, by this way an explanation is proposed for the measured increase of the thermal quenching and the decrease of the decay time of the yellow emission band with increasing Mn concentration. Durch Elektronenstrahl-Verdampfung hergestellte ZnS: Mn-Dunnschichten mit hohen Mn-Konzentrationen zwischen 2 und 6 mol% werden durch Emissions-, Anregungs- und Abkling-messungen der Photolumineszenz im Temperaturbereich von 28 bis 300 K untersucht. Es werden die ubliche gelbe und eine zusltzliche rote Emissionsbande mit dem gleichen Anregungsspektrum gefunden analog zu Ergebnissen fur hoch Mn-dotierte ZnS-Einkristalle. Die beobachtete charakteristische Temperatur- und Mn-Konzentrationsabhiingigkeit beider Banden wird quantitativ diskutiert auf der Grundlage eines Effektivlebensdauer-Modells, das strahlungslose Resonanz-energieubertragung von den primar angeregten Mn2+-Ionen uber mehrere andere Mn2+-Ionen durch einen Austauschmechanismus annimmt, die schliefilich zu den rot-emittierenden bzw. zu strahlungslosen Zentreri fuhrt. Damit wird insbesondere eine Erklarung fur die gemessene Zunahme der thermischen Tilgung und die Abnahme der Abklingzeit der gelben Emissionsbande mit wachsen-der Mn-Konzentration vorgeschlagen.

Automated image analysis of gliomas an objective and reproducible method for tumor grading

Abstract: A system of automated microscopic picture analysis was used in an examination of 272 gliomas (70 glioblastomas, 91 astrocytomas, 56 pilocytic astrocytomas or spongioblastomas, and 55 oligodendrogliomas). The specimens were prepared as Feulgen sections, 4μm in thickness. Thirteen morphometricdensitometric parameters of tumor cell nuclei were tested together with two mitotic parameters. Objective and reproducible data on numerical nuclear density (KRNZ, AREA), nuclear size (KOFL, KFRL, P250), nuclear shape (FOFK, FOFR, P150), optical density (EXTU, EXTS, EXSR, EXTM, EXMR), and mitotic activity (MITZ, VHMK) of the gliomas were obtained from the morphometric-densitometric parameters. All gliomas but glioblastomas were subdivided by four tumor grades. The morphometric-densitometric and mitotic data recorded were statistically checked, depending on tumor grade (Student'st-test, Wilcoxon's test, α=0.05). Numerical nuclear density, deformation of nuclei, and mitotic activity were found to grow with significance along with increasing tumor grade up to glioblastoma. The relative standard deviation (SD) of nuclear size (KFRL), relative SD of shape factors (FOFR), and relative SD of extinction sums (EXSR) are high-accuracy parameters for the pathologist to describe variability of sizes, polymorphism, and polychromasia of nuclei. These parameters show a significant increase of values in parallel with rising tumor grades, with maximum values being recordable from cases of glioblastomas. In cases of astrocytomas, optical values of nuclei decrease along with rising tumor grade. The data thus obtained were used as reference values for objective, reproducibel automatic glioma grading. The classifier method, described in an earlier publication, proved to be more effective than the regression method.

Crystal growth of PbTe and (Pb, Sn)Te by the bridgman method and by THM

Abstract: Synthesis and growth of PbTe and (Pb, Sn)Te single crystals by the Bridgman method and by the Travelling Heater Method (THM) from Te-rich solutions are described It is to be seen from comparative investigations that seeded THM growth reproducibly provides oriented single-crystalline ingots free of low-angle grain boundaries and with etch pit densities of 8-12 × 104 cm-2 All the materials were p-type with carrier concentrations from 1 to 2 × 1018 cm-3