Calcium-induced membrane microdomains trigger plant phospholipase D activity

Plant alpha-type phospholipase D proteins are calcium-dependent, lipolytic enzymes. The morphology of the aggregates of their phospholipid substrate fundamentally defines the interaction between the enzyme and the surface. Here we demonstrate that the Ca(2+)-induced generation of membrane microdomains dramatically activates alpha-type phospholipase D from white cabbage. 500-fold stimulation was observed upon incorporation of 10 mol % 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphate (POPA) into 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) vesicles in the presence of Ca(2+) ions. Enhanced association of PLDalpha2 with phospholipid surfaces containing anionic components was indicated by lag phase analysis and film balance measurements. Differential scanning calorimetry showed that the POPA-specific activation correlates with the phase behavior of the POPC/POPA vesicles in the presence of Ca(2+) ions. We conclude from the results that the Ca(2+)-induced formation of POPA microdomains is the crucial parameter that facilitates the binding of PLD to the phospholipid surface and suggest that this effect serves as a cellular switch for controlling PLD activity.     

Bulk superconductivity at 38 K in a molecular system

C(60)-based solids are archetypal molecular superconductors with transition temperatures (Tc) as high as 33 K (refs 2-4). Tc of face-centred-cubic (f.c.c.) A(3)C(60) (A=alkali metal) increases monotonically with inter C(60) separation, which is controlled by the A(+) cation size. As Cs(+) is the largest such ion, Cs(3)C(60) is a key material in this family. Previous studies revealing trace superconductivity in Cs(x)C(60) materials have not identified the structure or composition of the superconducting phase owing to extremely small shielding fractions and low crystallinity. Here, we show that superconducting Cs(3)C(60) can be reproducibly isolated by solvent-controlled synthesis and has the highest Tc of any molecular material at 38 K. In contrast to other A(3)C(60) materials, two distinct cubic Cs(3)C(60) structures are accessible. Although f.c.c. Cs(3)C(60) can be synthesized, the superconducting phase has the A15 structure based uniquely among fullerides on body-centred-cubic packing. Application of hydrostatic pressure controllably tunes A15 Cs(3)C(60) from insulating at ambient pressure to superconducting without crystal structure change and reveals a broad maximum in Tc at approximately 7 kbar. We attribute the observed Tc maximum as a function of inter C(60)separation--unprecedented in fullerides but reminiscent of the atom-based cuprate superconductors--to the role of strong electronic correlations near the metal-insulator transition onset.     

A simple fluorescence-spectroscopic membrane translocation assay

We have established a combination of fluorescence-spectroscopic uptake, release, and dilution experiments as a powerful tool for studying the translocation of fluorescent compounds across lipid membranes, demonstrating this through intrinsic tryptophan fluorescence for the interaction of the cell-penetrating peptide penetratin with phospholipid membranes, for which conflicting results have been reported. We found that penetratin is not membrane-permeant under the conditions used here. To confirm this finding and to validate the approach, we also employed an established titration-calorimetric method, the results of which were in excellent agreement with a thermodynamic analysis of the fluorescence-spectroscopic experiments. Further support was provided by a comparison with published data obtained under similar conditions by using a variety of techniques. Unlike these methods, however, the new approach allows consistent and simultaneous assessment of membrane binding and transbilayer movement without depending on extrinsic labels attached to the molecule of interest or on reporter moieties inserted into the lipid membrane.     

Interaction of a Tat substrate and a Tat signal peptide with thylakoid lipids at the air-water interface

The Tat machinery enables folded proteins to be translocated across biological membranes. In vitro studies have shown that Tat substrates can interact with membranes prior to translocation. In this study we investigated the initial states of this interaction with thylakoid lipid monolayers at the air-water interface by using monolayer techniques combined with infrared reflection-absorption spectroscopy (IRRAS). We used enhanced green fluorescent protein (EGFP) as a model substrate and the signal peptide SP16 from the 16 kDa protein of the spinach oxygen-evolving complex (OEC16). We found that the signal peptide is essential for the interaction of the model substrate with lipid monolayers. IRRA spectroscopy showed an increased amount of α-helical secondary structure elements for the chimeric model substrate i16/EGFP (SP16 fused to EGFP) compared with EGFP; this can be attributed to the signal peptide.     

Rate‐based‐Modellierung von CO2‐Absorptionskolonnen mit Anstaupackungen

The efficiency of columns for fluid separation can be increased by the application of sandwich packings. During the operation, different load‐dependent regimes with peculiar separation performance arise. In order to account for the effects of the individual flow regimes in a single model, both separation performance measurements and tomographic imaging are applied. A rate‐based model is presented, which takes the heterogeneous regimes in sandwich packings into account by means of appropriate correlations. The model is tested with experimental data for CO₂ absorption.     

Molecular beam epitaxy of InGaN thin films on Si(111): Effect of substrate nitridation

The effect of silicon nitridation on structural quality, indium incorporation, and electrical properties of the InGaN/Si heterojunctions is investigated. A series of In_xGa_1 − xN (x = 0-0.32) thin films are grown directly on Si(111) substrates, with and without a Si_xN_y surface layer, by plasma-assisted molecular beam epitaxy. The crystalline quality is higher and the indium incorporation is increased when the In_xGa_1 − xN thin films are grown with the intentional Si_xN_y buffer. These observations are explained by the reduced local elastic stress at the interface and N-polarity of the surface, both of which promote the incorporation of In. The obtained n-In_xGa_1 − xN/p-Si (x = 0.2-0.3) heterojunctions exhibit a nearly ohmic behavior, and the series resistance is higher for the Si_xN_y-containing junctions. Our results suggest that unlike the amorphous Si_xN_y region spontaneously formed during direct deposition of III-nitrides on Si, the Si_xN_y layer obtained by high-temperature annealing of Si(111) in nitrogen atmosphere is beneficial to the In_xGa_1 − xN deposition.     

Thermodynamic Characteristics of A Human Insulin-Deae-Dextran Complex Entrapped in Liposomes

Binding parameters were measured for a study of in vitrocomplexation interaction of human insulin with diethylaminoethyl (DEAE) dextran polymer by a diaultrafiltration (rapid dialysis). The complex was found to have appearent affinity constants of 22.9, 3.2 and 1.5 M^-1 at 25^deg C, 37^deg C and 45^deg C respectively in 0.067 M phosphate buffer at pH 7.4. The complexation reaction was found to be exothermic with an enthalpy change (AH) of 26 kcalhole. Differential scanning calorimetry (DSC) was used to obtain the temperatures and enthalpies for the insulin denaturation process in the presence of the DEAE-dextran polymer and liposomal membranes. The human insulin-DEAE-dextran complex appears to have a higher denaturation temperature with a higher denaturation enthalpy than the free human insulin in 0.067 M phosphate buffer at pH 7.4 solution. The uncomplexed human insulin entrapped in dimyristoyl phosphatidylcholine (DMPC) liposomes and neutral liposomes (DMPC/cholesterol = 1 : 1) did not differ significantly in temperature and enthalpy of denaturation from the unentrapped protein. Conversely, the complexed insulin entrapped in liposomes indicated an unchanged denaturation temperature but a lower denaturation enthalpy compared to the complexed human insulin not entrapped. The complexed human insulin entrapped in positively charged liposomes prepared from DMPC/cholesterol/stearylamine in the molar ratio of 7:2:1 showed a slight change in denaturation temperatures and lower denaturation enthalpies than the complexed protein not entrapped whereas the uncomplexed human insulin gave three peaks of different denaturation temperatures and enthalpies.     

Der Rückstreuquerschnitt des semiinfiniten Kreiskegels

Übersicht In dieser Arbeit beschäftigen wir uns mit der numerischen Berechnung des Rückstreuquerschnittes des semiinfiniten Kreiskegels. Wir behandeln sowohl den Fall der Beugung skalarer Wellen am schallweichen und schallharten Kreiskegel als auch den der Beugung elektromagnetischer Wellen am ideal leitenden Kreiskegel. Unter Zuhilfenahme des Eulerschen Summatiosverfahrens werden die über die Lösung der jeweiligen Randwertprobleme gewonnenen Multipolentwicklungen der Rückstreuquerschnitte für alle Kegelöffnungswinkel numerisch ausgewertet und mit bekannten analytischen Näherungsausdrücken für spitze und stumpfe Kegel verglichen. Wir werden u. a. zeigen, daß die physikalisch optische Näherungsmethode im Falle des Kreiskegels den richtigen Radarrückstreuquerschnitt liefert.

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Backscattering cross section of the semi-infinite circular cone

Contents This paper deals with the numerical calculation of the nose-on backscattering cross section of the semi-infinite circular cone. We examine both the diffraction of an incident scalar wave by a soft or a hard cone and the diffraction of an electromagnetic wave by a perfectly conducting cone. With the help of a special summation technique —the Eulersummation — we evaluate these series expansions and compare the results with the well known analytic approximation formulae for wide angle and narrow angle cones. For example we will show that the method of Physical Optics leads to the exact radar back-scattering cross section of the circular cone.

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