Formation of anaphylatoxin in human serum

Zusammenfassung Es ist möglich, auch in menschlichem Serum eine Anaphylatoxinbildung (AT) durch Kontaktaktivierung oder Kobragift zu induzieren. Wegen der geringen Mengen, die entstehen, muss das wirksame Prinzip vor dem biologischen Nachweis angereichert werden. Menschliches AT verhält sich in allen untersuchten Eigenschaften wie AT aus anderen Plasmaarten. Es unterscheidet sich von dem darmkontrahierenden Spaltprodukt aus der menschlichen Komplementkomponente C3, das mithin nicht als AT angesprochen werden kann.     

Light-avoidance-mediating photoreceptors tile the Drosophila larval body wall

Photoreceptors for visual perception, phototaxis or light avoidance are typically clustered in eyes or related structures such as the Bolwig organ of Drosophila larvae. Unexpectedly, we found that the class IV dendritic arborization neurons of Drosophila melanogaster larvae respond to ultraviolet, violet and blue light, and are major mediators of light avoidance, particularly at high intensities. These class IV dendritic arborization neurons, which are present in every body segment, have dendrites tiling the larval body wall nearly completely without redundancy. Dendritic illumination activates class IV dendritic arborization neurons. These novel photoreceptors use phototransduction machinery distinct from other photoreceptors in Drosophila and enable larvae to sense light exposure over their entire bodies and move out of danger.     

Potentiation of haemolysis by the combined action of phospholipase A and a basic peptide containing S-S-bonds (Viscotoxin B)

Zusammenfassung Viscotoxin B, ein basisches Peptid mit Disulfidgruppen, zeigt in der Hämolyse den gleichen synergistischen Effekt mit Phospholipase A wie der direkt lytische Faktor des Kobragiftes. Dieses Ergebnis stützt die Hypothese, dass Zellmembranen durch Reaktionen ihrer Protein-SH-Gruppen so verändert werden können, dass Phospholipase A sonst unzugängliche Membranphospholipide angreift.

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We thank MissAstrid Jörgensen for skilful technical assistance, and Dr.G. Samuelsson for viscotoxin B.     

Serienbestimmung der Phospholipase-A-Aktivität in chromatographischen Fraktionen

Summary A simple assay is described for phospholipase A in chromatographic fractions. 0.01 ml of the fraction is added to 1 ml of a 1% solution of purified lecithin in ether (100 vol) — picoline (10 vol) — 4.5 mmol CaCl₂ (1 vol). The presence of phospholipase A is indicated by the appearance of a turbidity due to precipitation of lysolecithin. The lag period until precipitation occurs gives an indication of the relative concentration of enzyme present.     

Attractive and repulsive Fermi polarons in two dimensions

The dynamics of a single impurity in an environment is a fundamental problem in many-body physics. In the solid state, a well known case is an impurity coupled to a bosonic bath (such as lattice vibrations); the impurity and its accompanying lattice distortion form a new entity, a polaron. This quasiparticle plays an important role in the spectral function of high-transition-temperature superconductors, as well as in colossal magnetoresistance in manganites. For impurities in a fermionic bath, studies have considered heavy or immobile impurities which exhibit Anderson's orthogonality catastrophe and the Kondo effect. More recently, mobile impurities have moved into the focus of research, and they have been found to form new quasiparticles known as Fermi polarons. The Fermi polaron problem constitutes the extreme, but conceptually simple, limit of two important quantum many-body problems: the crossover between a molecular Bose-Einstein condensate and a superfluid with BCS (Bardeen-Cooper-Schrieffer) pairing with spin-imbalance for attractive interactions, and Stoner's itinerant ferromagnetism for repulsive interactions. It has been proposed that such quantum phases (and other elusive exotic states) might become realizable in Fermi gases confined to two dimensions. Their stability and observability are intimately related to the theoretically debated properties of the Fermi polaron in a two-dimensional Fermi gas. Here we create and investigate Fermi polarons in a two-dimensional, spin-imbalanced Fermi gas, measuring their spectral function using momentum-resolved photoemission spectroscopy. For attractive interactions, we find evidence for a disputed pairing transition between polarons and tightly bound dimers, which provides insight into the elementary pairing mechanism of imbalanced, strongly coupled two-dimensional Fermi gases. Additionally, for repulsive interactions, we study novel quasiparticles--repulsive polarons--the lifetime of which determines the possibility of stabilizing repulsively interacting Fermi systems.