2,391 research outputs found
Structure and kinetics of chemically cross-linked protein gels from small-angle X-ray scattering
Glutaraldehyde (GA) reacts with amino groups in proteins, forming
intermolecular cross-links that, at sufficiently high protein concentration,
can transform a protein solution into a gel. Although GA has been used as a
cross-linking reagent for decades, neither the cross-linking chemistry nor the
microstructure of the resulting protein gel have been clearly established. Here
we use small-angle X-ray scattering (SAXS) to characterise the microstructure
and structural kinetics of gels formed by cross-linking of pancreatic trypsin
inhibitor, myoglobin or intestinal fatty acid-binding protein. By comparing the
scattering from gels and dilute solutions, we extract the structure factor and
the pair correlation function of the gels. The protein gels are spatially
heterogeneous, with dense clusters linked by sparse networks. Within the
clusters, adjacent protein molecules are almost in contact, but the protein
concentration in the cluster is much lower than in a crystal. At the 1 nm
SAXS resolution, the native protein structure is unaffected by cross-linking.
The cluster radius is in the range 10 - 50 nm, with the cluster size determined
mainly by the availability of lysine amino groups on the protein surface. The
development of structure in the gel, on time scales from minutes to hours,
appears to obey first-order kinetics. Cross-linking is slower at acidic pH,
where the population of amino groups in the reactive deprotonated form is low.
These results support the use of cross-linked protein gels in NMR studies of
protein dynamics and for modeling NMR relaxation in biological tissue.Comment: 16 pages, 11 figure
Weak self-interactions of globular proteins studied by small-angle X-ray scattering and structure-based modeling
We investigate protein-protein interactions in solution by small-angle X-ray
scattering (SAXS) and theoretical modeling. The structure factor for solutions
of bovine pancreatic trypsin inhibitor (BPTI), myoglobin (Mb), and intestinal
fatty acid-binding protein (IFABP) is determined from SAXS measurements at
multiple concentrations, from Monte Carlo simulations with a coarse-grained
structure-based interaction model, and from analytic approximate solutions of
two idealized colloidal interaction models without adjustable parameters. By
combining these approaches, we find that the structure factor is essentially
determined by hard-core and screened electrostatic interactions. Other soft
short-ranged interactions (van der Waals and solvation-related) are either
individually insignificant or tend to cancel out. The structure factor is also
not significantly affected by charge fluctuations. For Mb and IFABP, with small
net charge and relatively symmetric charge distribution, the structure factor
is well described by a hard-sphere model. For BPTI, with larger net charge,
screened electrostatic repulsion is also important, but the asymmetry of the
charge distribution reduces the repulsion from that predicted by a charged
hard-sphere model with the same net charge. Such charge asymmetry may also
amplify the effect of shape asymmetry on the protein-protein potential of mean
force.Comment: 15 pages, 8 figure
Beurteilung der Nährstoffversorgung bei hochleistenden Tieren – hier Mastbroiler – mit Öko-Futtermitteln
Das Ziel der beiden Versuche des Forschungsauftrages 02OE023 „Beurteilung der Nährstoffversorgung bei hochleistenden Tieren – hier Mastbroiler – mit Öko-Futtermitteln“ bestand darin, den Einfluss einer gestaffelten Protein- und Energieversorgung langsamwachsender Broiler auf Wachstumsmerkmale und Ganzkörperzusammensetzung zu prüfen. Für die Untersuchungen standen 469 (Versuch 1) bzw. 384 (Versuch 2) männliche Broiler der Herkunft Hubbard ISA 257 zur Verfügung. Die Versuche, die eine Länge von 56 bzw. 84 Tage hatten, wurden in ein, zwei oder drei Phasen (1. – 35., 36. – 56., 57. – 84. Tag) eingeteilt.
Die Broiler erreichten im Versuch 2 Mastendmassen von über 4 kg nach 84 Tagen durch eine hohe Proteinversorgung von 23 % im Starterfutter (0,4 % Methionin) vom 1. – 35. Lebenstag sowie 21 % (0,37 % Methionin) im Nachfolgefutter, um insbesondere eine bedarfsgerechtere Methioninkonzentration im Futter, das sich aus Futtermitteln aus dem ökologischen Landbau zusammensetzte, zu realisieren. Eine Energiekonzentration von 12 MJ ME pro kg (Trockensubstanz) wurde dabei dem höheren Energiebedarf der bewegungsaktiven Broiler gerecht. Eine Fütterung der langsamwachsenden Broiler in zwei oder drei Phasen (1. - 35., 36. – 56., 57. – 84. Tag) und einer damit verbundenen besseren Anpassung der Proteinkonzentration im Futter an den Bedarf der Tiere erwies sich als geeignete Fütterungstechnik. Nach einer intensiven Fütterung der Broiler mit höheren Proteingehalten im ökologischen Futter bzw. durch Fütterung eines optimierten kommerziellen Futters zeigte sich, dass das der tägliche Zuwachs der Broiler nach 56 Tagen Mast rückgängig war. Der Futteraufwand, der bei den herkömmlich gefütterten Broilern bis zum 56. Tag bei 1,8 kg/kg und den intensiv-ökologisch gefütterten Broilern bei 2,0 kg/kg lag, verschlechterte sich in den folgenden 4 Wochen auf 3,2 kg/kg bzw. 3,4 kg/kg. Erste Hinweise auf eine mögliche Bedeutung für den Einsatz von Kräutern, die ätherische Öle mit einem hohen Anteil an Carvacrol enthalten, im ökologischen Broilerfutter gaben die Wachstumsergebnisse der Broiler, deren Futter mit einem 1 % getrocknetem Bohnenkraut angereichert war
Automata-based Optimization of Interaction Protocols for Scalable Multicore Platforms (Technical Report)
Multicore platforms offer the opportunity for utilizing massively parallel resources. However, programming them is challenging. We need good compilers that optimize commonly occurring synchronization/interaction patterns. To facilitate optimization, a programming language must convey what needs to be done in a form that leaves a considerably large decision space on how to do it for the compiler/run-time system.
Reo is a coordination-inspired model of concurrency that allows compositional construction of interaction protocols as declarative specifications. This form of protocol programming specifies only what needs to be done and leaves virtually all how-decisions involved in obtaining a concrete implementation for the compiler and the run-time system to make, thereby maximizing the potential opportunities for optimization. In contrast, the imperative form of protocol specification in conventional concurrent programming languages, generally, restrict implementation choices (and thereby hamper optimization) due to overspecification.
In this paper, we use the Constraint Automata semantics of Reo protocols as the formal basis for our optimizations. We optimize a generalization of the producer-consumer pattern, by applying CA transformations and prove the correctness of the transforms
Linguistics
Contains reports on three research projects.National Science Foundation (Grant GP-2495)National Institutes of Health (Grant MH-04737-04)U. S. Air Force. Electronics Systems Division (Contract AFl9(628)-2487)National Aeronautics and Space Administration (Grant NsG-496
Linguistics
Contains reports on two research projects.National Institute of Mental Health (Grant 5 P01 MH-13390-05)National Institute of Mental Health (Grant 5 TO1 HD-00111-06
Speech Communication
Contains research objectives and reports on two research objectives.U.S. Air Force (Air Force Cambridge Research Center, Air Research and Development Command) under Contract AF19(604)-6102National Science Foundatio
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