PraemiaDie Nobelpreise 1955 für Physik,Chemie und Medizin

Ohne Zusammenfassung     

Chemische Kopplung von Hexokinase aus Hefe an Sephadex

Summary Yeast hexokinase was coupled to Sephadex by means of cyanogen bromide. The activity of the fixed enzyme was 2% of that before coupling. The activity of the noncoupled part of the enzyme was also decreased to the same degree. This decrease cannot be caused by the coupling reaction itself. The Michaelis-constants and the pH-activity curve of the coupled enzyme do not differ significantly from that of the free enzyme.     

Die Bestimmung von Dibenamin im biologischen Material

Summary In order to identify the presence of dibenamine and dibenamine-like compounds in biological substances (urine, sera) bromine cresol purple was used as a formative element in the adduction of dyestuff (i.e. as Farbstoffadduktbildner). This method permits a more simplified and more sensitive process of work than that suggested byBrodie and his collaborators.     

Designing metallic glass matrix composites with high toughness and tensile ductility

The selection and design of modern high-performance structural engineering materials is driven by optimizing combinations of mechanical properties such as strength, ductility, toughness, elasticity and requirements for predictable and graceful (non-catastrophic) failure in service. Highly processable bulk metallic glasses (BMGs) are a new class of engineering materials and have attracted significant technological interest. Although many BMGs exhibit high strength and show substantial fracture toughness, they lack ductility and fail in an apparently brittle manner in unconstrained loading geometries. For instance, some BMGs exhibit significant plastic deformation in compression or bending tests, but all exhibit negligible plasticity (<0.5% strain) in uniaxial tension. To overcome brittle failure in tension, BMG-matrix composites have been introduced. The inhomogeneous microstructure with isolated dendrites in a BMG matrix stabilizes the glass against the catastrophic failure associated with unlimited extension of a shear band and results in enhanced global plasticity and more graceful failure. Tensile strengths of approximately 1 GPa, tensile ductility of approximately 2-3 per cent, and an enhanced mode I fracture toughness of K(1C) approximately 40 MPa m(1/2) were reported. Building on this approach, we have developed 'designed composites' by matching fundamental mechanical and microstructural length scales. Here, we report titanium-zirconium-based BMG composites with room-temperature tensile ductility exceeding 10 per cent, yield strengths of 1.2-1.5 GPa, K(1C) up to approximately 170 MPa m(1/2), and fracture energies for crack propagation as high as G(1C) approximately 340 kJ m(-2). The K(1C) and G(1C) values equal or surpass those achievable in the toughest titanium or steel alloys, placing BMG composites among the toughest known materials.     

A young source for the Hawaiian plume

Recycling of oceanic crust through subduction, mantle upwelling, and remelting in mantle plumes is a widely accepted mechanism to explain ocean island volcanism. The timescale of this recycling is important to our understanding of mantle circulation rates. Correlations of uranogenic lead isotopes in lavas from ocean islands such as Hawaii or Iceland, when interpreted as model isochrons, have yielded source differentiation ages between 1 and 2.5?billion years (Gyr). However, if such correlations are produced by mixing of unrelated mantle components they will have no direct age significance. Re-Os decay model ages take into account the mixing of sources with different histories, but they depend on the assumed initial Re/Os ratio of the subducted crust, which is poorly constrained because of the high mobility of rhenium during subduction. Here we report the first data on (87)Sr/(86)Sr ratios for 138 melt inclusions in olivine phenocrysts from lavas of Mauna Loa shield volcano, Hawaii, indicating enormous mantle source heterogeneity. We show that highly radiogenic strontium in severely rubidium-depleted melt inclusions matches the isotopic composition of 200-650-Myr-old sea water. We infer that such sea water must have contaminated the Mauna Loa source rock, before subduction, imparting a unique 'time stamp' on this source. Small amounts of seawater-derived strontium in plume sources may be common but can be identified clearly only in ultra-depleted melts originating from generally highly (incompatible-element) depleted source components. The presence of 200-650-Myr-old oceanic crust in the source of Hawaiian lavas implies a timescale of general mantle circulation with an average rate of about 2 (±1)?cm?yr(-1), much faster than previously thought.     

Crystal structure of opsin in its G-protein-interacting conformation

Opsin, the ligand-free form of the G-protein-coupled receptor rhodopsin, at low pH adopts a conformationally distinct, active G-protein-binding state known as Ops*. A synthetic peptide derived from the main binding site of the heterotrimeric G protein-the carboxy terminus of the alpha-subunit (GalphaCT)-stabilizes Ops*. Here we present the 3.2 A crystal structure of the bovine Ops*-GalphaCT peptide complex. GalphaCT binds to a site in opsin that is opened by an outward tilt of transmembrane helix (TM) 6, a pairing of TM5 and TM6, and a restructured TM7-helix 8 kink. Contacts along the inner surface of TM5 and TM6 induce an alpha-helical conformation in GalphaCT with a C-terminal reverse turn. Main-chain carbonyl groups in the reverse turn constitute the centre of a hydrogen-bonded network, which links the two receptor regions containing the conserved E(D)RY and NPxxY(x)(5,6)F motifs. On the basis of the Ops*-GalphaCT structure and known conformational changes in Galpha, we discuss signal transfer from the receptor to the G protein nucleotide-binding site.