Showing papers by "University of Marburg published in 1975"

Direct measurement by pH-microelectrode of the pH microclimate in rat proximal jejunum

Abstract: The existence of a region of low pH juxtaposed to the proximal jejunum has been proposed to explain anomalies in the transfer of weakly-ionizing substances: yet no direct evidence for this layer exists. Surface electrode studies on everted sacs revealed the existence of the layer and estimated the pH to be at least 5.5 when the buffer pH is 7.2. With 60 $\mu $m long tip microelectrodes, a value of 6.0 was obtained, however, the dimensions of this microclimate are uncertain. Optical experiments with pH-indicators using a microscope of 20 $\mu $m resolving power and flat strips in vitro, failed to detect this layer. With the dimensions of the tip microelectrode known, values are given for the maximum possible microclimate pH for a corresponding microclimate depth. The significance of the pH microclimate to malabsorption is briefly discussed.

Histamine release in man.

Abstract: (1) Histamine release in man could be demonstrated using the fluorometric histamine assay in plasma as a reliable test. (2) Histamine release in animals may be relevant in some cases for human subjects, as shown for anaesthetic drugs and plasma substitutes on gelatin basis. In other cases histamine release in animals may not be relevant for man as demonstrated for dextran. (3) Even if a small histamine release could be detected in human subjects as in the case of dextran this must not implicate that also in severe anaphylactoid incidents histamine release is the cause of these events. (4) Plasma histamine determinations led to a much better understanding of histamine-induced reactions in human subjects than other techniques and — which is the most important advantage — increase the possibility to differentiate between histamine-induced reactions and anaphylactoid reactions caused by other mediators. The suggestion in former time that histamine might be involved in all types of ‘allergic’ reactions induced a histamine philosophy. Differentiation, however, gives histamine its place at least in human pathophysiology.

Thermopower calculation for variable range hopping — application to α-Si

Abstract: An expression for the thermopower S in the variable range hopping regime near the Fermi energy is derived. This allows the calculation of S for an arbitrary density of states, provided the localisation length, α−1, is kept constant. An application is made to estimate the density of states function of amorphous Si from conductivity and thermopower data. Ein Ausdruck fur die Thermokraft S im Bereich des Variable-Range-Hopping am Ferminiveau wird hergeleitet. Der Formalismus erlaubt die Berechnung von S fur beliebige Modelle der Zustandsdichte. Die Lokalisierungslange der Zustande, α−1, wird dabei als konstant angenommen. Der Formalismus wird zu einer Abschatzung der Form der Zustandsdichtefunktion in amorphem Silizium aus experimentellen Leitfahigkeits- und Thermokraftdaten verwendet.

Comparative effect of heparin on RNA synthesis of isolated rat-liver nucleoli and purified RNA polymerase A.

Abstract: The polyanion heparin has been employed to study the interaction of rat liver DNA-dependent RNA polymerase A and its template under various conditions. Heparin very efficiently inhibits polymerase molecules, which are not bound to DNA or are associated with the template in a loose, i.e., non-specific fashion. Purified nucleoli, isolated from rat liver nuclei, contain RNA polymerase A in abundant quantities of which only a portion is bound in a transcriptional complex. Excess enzyme, which is contained in the nucleolus in a quasi free form, can be transferred to an exogenously added template and can be completely inhibited by the prior addition of heparin. The enzyme contained in a transcriptional complex, however, initiated in vivo and completing these RNA chains in vitro, is fully resistant to heparin. In contrast to these results it has been found that RNA polymerase A extracted from nuclei and purified by various chromatographic steps does not form heparin-resistant complexes, even after the enzyme has been bound to the DNA template. Moreover it has been found that purified RNA polymerase A transcribes truly native DNA extremely poorly, indicating that the enzyme is highly deficient in the act of initiation on duplex DNA. It is therefore questionable whether the interaction of the purified enzyme and isolated DNA represents binding to true initiation complexes as is observed in the intact nucleolus.

DNA‐Dependent RNA Polymerase C

Abstract: DNA-dependent RNA-polymerase C, initially shown to exist in rat liver tissue and characterized by its sensitivity toward high concentrations of α-amanitin, has been shown to exist in HeLa cells and to be present in variable amounts in the nucleus of the rat liver cell. Enzyme C has been shown to co-chromatograph with nucleolar RNA polymerase A (or I) on DEAE-cellulose and can clearly be separated from the latter by chromatography on DEAE-Sephadex. It is possible that RNA polymerase C may occur in multiple forms although the significance of this finding is unclear at present. From its similar chromatographic properties and sensitivity toward α-amanitin it is possible that RNA polymerase C corresponds to polymerase III.

Pre-equilibrium and heat conduction in nuclear matter

Abstract: A model for pre-equilibrium nucleon emission is formulated in terms of diffusion of heat in nuclear matter. A strong asymmetry in the angular distribution of evaporation products is predicted.

Induction of dopa (3,4-dihydroxyphenylalanine) decarboxylase in blowfly integument by ecdysone. A demonstration of synthesis of the enzyme de novo.

Abstract: The activity of the enzyme dopa (3,4-dihydroxyphenylalanine) decarboxylase, present in the epidermis cells of blowfly larvae, increases during the late third instar under the influence of the steroid hormone, ecdysone. By using the double-labelling technique and immune precipitation with univalent antibody to dopa decarboxylase, we demonstrated that the increase in enzyme activity was due to a stimulation of synthesis of enzyme molecules de novo. In this respect, the action of ecdysone is similar to the action of other steroid hormones.

Structure and optical properties of polycrystalline evaporated tetracene films

Abstract: Experimentally determined differences between the p-band absorption spectra of polycrystalline tetracene films and single crystals are shown to be caused by the oriented polycrystalline structure, which is described. The film spectra can be completely understood on the basis of single crystal absorption data when the measurement with unpolarized light and two wavelength-dependent diffraction effects are taken into account. These are due to the fact that a film composed of unisotropic microcrystals can act both as an amplitude and a phase grating.

Translation of mRNA for 3,4‐Dihydroxyphenylalanine Decarboxylase Isolated from Epidermis Tissue of Calliphora vicina R.‐D. in an Heterologous System

Abstract: RNA was isolated from the epidermis of Calliphora vicina larvae by phenol–chloroform extraction. The RNA sedimenting in sucrose gradients between 5 and 18 S was submitted to chromatography on oligo(dT)-cellulose columns. The fraction binding to the oligo(dT) is able to stimulate protein synthesis in a system consisting of mouse liver ribosomal subunits, pH-5 factors from rat liver and initiation factors from rabbit reticulocytes. Optimal Mg2+ concentration for the translation of insect mRNA is 3.5 mM, that of K+ 76 mM. Initiation factors prepared from epidermis of Calliphora larvae are less efficient in the translation of insect mRNA than initiation factors isolated from reticulocytes. The pH-5 fraction from epidermis inhibits protein synthesis independent of the source of the mRNA fraction used. One of the proteins synthesized in the reconstituted system under the direction of insect mRNA has been identified as 3,4-dihydroxyphenylalanine (DOPA) decarboxylase by immunoprecipitation with specific antiserum against DOPA decarboxylase and comigration in dodecylsulphate-acrylamide electrophoresis with pure DOPA decarboxylase. Both mRNA from white prepupae and from 6–7-days-old larvae contain sequences coding for DOPA decarboxylase. However, white prepupae contains 3–4 times more DOPA decarboxylase-mRNA than 6–7-days-old larvae. The content of DOPA decarboxylase mRNA is proportional to the amount of active DOPA decarboxylase molecules present in the animals from which the mRNA was isolated.

Studies of the subunit structure of choleragen.

Abstract: The two choleragen protein constituents were isolated and characterized. Protein I has a molecular weight of approximately 54000. It consists of subunits of approximate molecular weight 10000. Protein II with molecular weight of approximately 32000 is cleaved by 2-mercaptoethanol into two fragments, protein II1 (N-terminal Asx, Mr= 25000) and protein II2 (N-terminal Ser, Mr= 7000) Proteins II1 and II2 could be recombined by oxidation to yield protein II. Upon treatment of choleragen with 2-mercaptoethanol protein II1 precipitates quantitatively. The remaining protein consisting of proteins I and II2, was quantitatively precipitated by ganglioside GGtet1. Of the separated choleragen subunit proteins, only protein I and not protein II complexed specifically with ganglioside GGtet1. The isolated proteins I and II were considerably less toxic in the skin test but almost full toxi-city was recovered after mixing the two proteins I and II. Antisera against protein I and protein II revealed no immuno-cross reactivity between the two proteins. Both antisera inhibited the biological effects of choleragen in the skin and ileal loop tests. A molecular model for the constitution of choleragen is proposed.

Electrical conductivity and excess volume of the liquid alloy system Li–Bi

Abstract: The paper presents new experimental results of the electrical conductivity and the excess volume of liquid lithium-bismuth mixtures in the concentration range between 4 and 26.8 at % Bi and at temperatures up to 1250°C. Pronounced changes of both conductivity and volume are observed in the vicinity of 25 at % Bi, where the phase diagram indicates the formation of the compound Li3Bi in the solid. The low conductivity of 5 · 102 Ω−1 cm−1 and the positive temperature coefficient at 24.3 at % Bi are not consistent with a metallic description of this alloy near the compound composition. A possible interpretation of the metal-nonmetal transition in relation to a change in chemical bonding is discussed for this liquid alloy. Since both liquid compounds Li and Bi are very corrosive at elevated temperatures a special experimental technique was necessary which is described in detail. Es werden neue Messungen der elektrischen Leitfahigkeit und des Exzes-Volumens von flussigen Li – Bi-Mischungen im Konzentrationsgebiet zwischen 4 und 26,8 Atomprozent Bi bei Temperaturen bis zu 1250°C beschrieben. Eine starke Konzentrationsabhangigkeit der Leitfahigkeit und des Volumens wird in der Nahe von 25 Atomprozent Bi, wo das Phasendiagramm die Bildung der Verbindung Li3Bi in der festen Phase andeutet, beobachtet. Die geringe Leitfahigkeit von 5 · 102 Ω−1 cm−1 und der positive Temperaturkoeffizient bei 24,3 Atomprozent Bi weisen auf nichtmetallisches Verhalten der Mischung bei der stochiometrischen Konzentration hin. Eine mogliche Erklarung des Metall-Nichtmetallubergangs durch Verbindungsbildung in der flussigen Mischung wird diskutiert. Da flussiges Li und flussiges Bi bei erhohten Temperaturen sehr korrosiv sind, war die Anwendung einer speziellen experimentellen Technik, die im Detail beschrieben wird, notwendig.

Adenine Nucleosides in Solution: Circular Dichroism Studies and Base Conformation

Abstract: Adenosine, AMP, S-adenosylhomocysteine, S-adenosylmethionine, aristeromycin and 25 other synthetic adenosine analogs modified in the 4' or 5' positions show certain groups of different circular dichroism (CD) spectra. Both positive and negative Cotton effects can occur in the long-wavelength part (250-270 nm) of the spectra. Molar ellipticities [theta] range from -6000 (in adenosine 5'-carboxylate) to +4000 deg. cm2 dmol-1 (in 5'-deoxy-5'iodoadenosine), including some compounds with small, polar 5'-substituents in which low-intensity bands are found in signed pairs. Most of these adenosine derivatives that have the same adenine chromophore and a ribofuranose moiety unsubstituted in the 2' and 3' positions prefer an anti-conformation of the adenine base, as evidenced by proton magnetic resonance spectroscopy. In the majority of cases, electronic perturbations of the chromophore or major alterations of the assymmetric sugar residue can be excluded as sources of the CD variations. Therefore a correlation of the long-wavelength CD bands with the glycosyl torsion angle phiCN is suggested, where the gauche, gauche/anti combination which is typical of AMP in the crystal and in solution (phiCN approximately -40degrees, [theta] negative) is one reference point and a region for phiCN = 0degrees ([theta] positive) is assigned to compounds with space-filling substituents such as S-adenosylmethionine. Both negative and positive Cotton effects can be associated with the anti conformation range. Within this series, the base conformation of novel nucleoside structures could be predicted from CD measurements. The CD spectrum gives no indication, however, of whether a certain torsion angle is the result of a rigid structure (as in AMP) or the average value of a molecule with high rotational freedom (as in 5'-deoxyadenosine). The conformations of aristeromycin and 4'-thioadenosine are discussed in relation to adenosine, and a structure-determining effect of the 4' bridge atom is noted.

Effect of amodiaquine on gastric histamine methyltransferase and on histamine-stimulated gastric secretion.

Abstract: 1 Amodiaquine was found to be a potent inhibitor in vitro of gastric histamine methyltransferase from human and canine corpus and from pig antrum. The ID50 for the enzyme, purified from pig antrum mucosa by ultracentrifugation and chromatography on DEAE-cellulose, was 2.5 muM. 2 In six dogs with Heidenhanin pouches the maximum secretory response to histamine (40 mug/kg i.m.) was augmented by i.m. injection of amodiaquine. The augmentation depended on the dose of amodiaquine, the optimum effect (40% increase in volume of gastric juice, 80% in acid output) being achieved with 2 mg/kg. The maximum secretory response to betazole was also enhanced by amodiaquine. 3 It was suggested that amodiaquine may enhance the histamine and betazole stimulated gastric secretion by an inhibition of gastric histamine methyltransferase in vivo.

Three distinct forms of nuclear poly(A) polymerase.

Abstract: Poly(A) polymerase activities have been solubilized from rat liver nuclei and purified by chromatography on Bio-Gel A-1.5m, DEAE-Sephadex and CM-cellulose. Three distinct forms of nuclear poly(A) polymerase have been resolved by chromatography on CM-cellulose. According to their sequence of elution from CM-cellulose these enzyme activities have been termed A, B and C. Enzymes A and B are Mn2+-dependent, enzyme C requires Mg2+. With the same chromatographic step on CM-cellulose the Mn2+-dependent poly(A) polymerase activities were separated from a Mn2+-dependent enzyme system capable of synthesizing RNA-primed poly(U), poly(G) and poly(C). The effect of different nuclear and cytoplasmic RNA primers on the rate of poly(A) formation suggests enzyme A to be responsible for the elongation of preexisting poly(A) chains. The phosphorylated derivative of cordycepin, 3′-deoxyadenosine 5′-triphosphosphate (3′-dATP), which is known to inhibit nuclear poly(A) synthesis in vivo, also impairs poly(A) formation in vitro. It is shown that 3′-dATP very probably is not incorporated into poly(A) in vitro, suggesting that 3′-dATP primarily affects the catalytic activities of the poly(A) polymerase species rather than directly blocking chain elongation.

The Effect of Inhibitors on the Electron Flow Triggering Photo-Phobic Reactions in Cyanophyceae

Abstract: 1. Since photo-phobic reactions in the blue green alga Phormidium uncinatum seem to be triggered by changes of electron flow rates into or out of an electron pool situated in the electron transport chain between photo-system II and I, the effect of inhibitors affecting the electron transport chain has been studied. 2. Dose response curves of the phobic reaction have been measured by varying the trap energy in double beam light trap experiments with constant pairs of monochromatic light. From these dose response curves the effects of the inhibitors on both types of phobic reactions, i.e. exit reactions and entrance reactions, have been calculated. 3. Dibromothymoquinone (DBMIB) inhibits the electron transport between the electron pool and photosystem I by preventing the reoxidation of plastoquinone. The phobic entrance reaction, which results in an emptying of the light trap, is triggered by changes in the electron flow out of the pool; thus it is more effected by DBMIB than the exit reaction, which is mediated by the electron transport into the pool. 4. The phobic exit reaction, which results in accumulations in the light trap, is triggered by changes in the electron flow into the electron pool via photosystem II. 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) inhibits the electron transport near photosystem II; thus it affects the exit reaction more than the entrance reaction.