Obfuscation of allosteric structure-function relationships by enthalpy-entropy compensation

The pH and temperature dependence of the allosteric properties of phosphofructokinase (PFK) from Bacillus stearothermophilus have been studied from 5 to 9 and 6 to 40 degrees C, respectively. Throughout this pH and temperature range the allosteric ligands MgADP and phospho(enol)pyruvate (PEP) have no effect on kcat. The dissociation constants of the substrate, fructose 6-phosphate, and the allosteric ligands, as well as the absolute value of the coupling free energies between these ligands, all increase when the pH is raised, indicating that the inhibition by PEP and the activation by MgADP increase despite each ligand's somewhat lower affinity. However, the constituent coupling enthalpies and entropies substantially diminish in absolute value as pH is increased, suggesting that the magnitudes of molecular perturbations engendered by the binding of allosteric ligands do not correlate with the magnitudes of the functional consequences of those perturbations. Temperature and pH exert their influence on the observed allosteric behavior by changing the relative contributions made by the largely compensating DeltaH and TDeltaS terms to the coupling free energy.     

Reduced cardiac contractile responsiveness to isoproterenol in obese rabbits

Although obesity is characterized by increased sympathetic nervous system activity, there is often a paradoxical reduction in cardiovascular end-organ response to sympathetic stimulation. Mechanisms involved in reduced sympathetic responsiveness in obesity have not been well characterized. Therefore, we determined cardiac contractile responsiveness to beta-stimulation in the obese rabbit model using both isolated heart (IH) and isolated papillary muscle (IPM) preparations. Female New Zealand White rabbits were fed control (IH: n=9; IPM: n=6) or 10% fat diets (IH: n=9; IPM: n=7) for 12 weeks. Contractile responsiveness in the IH was determined using a modified Langendorff preparation to evaluate the dose-response relationship between isoproterenol and 1) peak developed pressure/g of left ventricular wet weight and 2) maximal rate of pressure development (+dP/dt/P). Contractile responsiveness in the IPM was determined using right ventricular papillary muscles to evaluate the dose-response relationship between isoproterenol and (1) peak developed tension (T)/mm2 cross-sectional area (CSA) and (2) maximal rate of tension development (dT/dt/CSA). In the IH, baseline and maximum developed pressure/g were reduced in obese rabbits by 37% and 31%, respectively (P< or =.05). In the IPM, baseline and maximum T/CSA responses were reduced in obese rabbits by 59% and 33%, respectively (P< or =.05). Potency of isoproterenol as reflected by the EC50 did not differ between lean and obese animals in either preparation. These results demonstrate that left ventricular contractility in obesity is reduced at baseline and in response to stimulation with isoproterenol and suggest that decreased responsiveness to beta-stimulation may be a factor in the obesity-related systolic dysfunction.     

Evaluation of the effects of omega-3 fatty acid-containing diets on the inflammatory stage of wound healing in dogs

OBJECTIVES: To ascertain the effects of dietary omega-3 (n-3) fatty acids on biochemical and histopathologic components of the inflammatory stage of wound healing. ANIMALS: 30 purpose-bred Beagles. PROCEDURE: Dogs were allotted to 5 groups of 6. Each group was fed a unique dietary fatty acid ratio of omega-6 to n-3--diet A, 5.3:1; diet B, 10.4:1; diet C, 24.1:1; diet D, 51.6:1; and diet E, 95.8:1. Dogs were fed once daily for 12 weeks, then biopsy specimens were taken from 4-day-old wounds of each dog and analyzed by gas chromatography-mass spectrometry for: prostaglandin E2 (PGE2) metabolites, and ratios of omega-6 to n-3 fatty acids, arachidonic acid (AA) to eicosapentaenoic acid (EPA), adrenic acid to docosahexaenoic acid, and PGE2 to prostaglandin E3 (PGE3) metabolites. RESULTS: Qualitative analysis was carried out on AA, EPA, adrenic acid, docosahexaenoic acid, and the major metabolite from the PGE2 and PGE3 pathway. These molecules were further quantified with respect to diet to determine significant differences. By analysis of the AA-to-EPA ratio, diet A was different from diets D and E and diets B and C were different from diet E (P < 0.05). By analysis of the PGE2-to-PGE3 metabolite ratio, diet A was different from diet E (P < 0.05). Though biochemical analysis indicated dietary dependence, histopathologic data indicated no significant difference with respect to diet groups. CONCLUSION: The biochemical component of the inflammatory stage of wound healing can be manipulated by diet. CLINICAL RELEVANCE: Omega-3 fatty acid-enriched diets can be used to control inflammation associated with dermatologic conditions.     

复杂技术产品的协同开发

以机床为例，介绍了一个计算机辅助产品开发的方案。应用该方法，在同步工程技术的基础上，能快速地实现复杂技术产品的协同开发，并使产品开发的风险最小。     

Electrooptic polarization modulation in multielectrode AlxGa1-xAs rib waveguides

A single mode rib waveguide (RWG) polarization modulator is described with a measured extinction ratio ≳27 dB, a power conversion ≈0.99, and a switching voltage of 12.5 V atlambda = 1.064 mum. The modulator is based on a modified stepDeltabeta-reversal configuration. Contact with CdO and an Au overlay ensures low optical losses (lsim1cm^-1) for both polarizations.     

Long-term hydrostatic strength characteristics of thermoplastics pipe

A method for developing long-term hydrostatic design stresses, defined as the estimated tensile stress in the wall of the pipe in the circumferential orientation due to internal hydrostatic pressure that can be applied continuously with a high degree of certainty that failure of the pipe will not occur, for thermoplastic pipe materials is described. The background information used to develop this method, data to confirm its validity, and several of its more important peculiarities are presented and discussed. The method treats hydrostatic stress–failure time test results by the method of least squares with time as the dependent variable. The long-trem performance of thermoplastic pipe materials is evaluated by stresses calculated for periods of 100,000 hours (11.43 years) and 50 years.     

Synthesis and regulation of leukaemia inhibitory factor in cultured bovine oviduct cells by hormones

Group II introns are large, self-splicing RNAs and mobile genetic elements that provide good model systems for studies of RNA folding. The structures and mechanistic functions of individual domains are being elucidated, and long-range tertiary interactions between the domains are being identified, thus helping to define the three-dimensional architecture of the intron.     

Rechtliche Implikationen zur Verwendung von Nanopartikeln in Lebensmitteln und Kosmetika

Zusammenfassung:  Die Verwendung von Nanopartikeln in Lebensmitteln und kosmetischen Mitteln ist anhand der lebensmittelrechtlichen bzw. der für Kosmetika geltenden Rechtsvorschriften zu beurteilen, da es keine nanotechnologischen Sonderregelungen gibt. Das Hauptproblem besteht dabei insoweit, die gegenw?rtig begrenzten Kenntnisse über m?gliche Gesundheitsrisiken sachgerecht unter den gegebenen Rechtsrahmen zu subsumieren. Damit geht die Frage einher, ob ein Defizit an naturwissenschaftlichen Erkenntnissen durch ein Mehr an „schützenden“ Regelungen kompensiert werden kann.

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Eingegangen: 29. Januar 2008; angenommen: 4. Februar 2008     

Simulation-based layout optimization for multi-station assembly lines

Journal of Intelligent Manufacturing - This article presents a novel approach for the automated 3D-layout planning of multi-station assembly lines. The planning method is based on a comprehensive...     

Characterization of prompt flash signatures using high-speed broadband diode detectors

Impact flash is a brief, intense flash of light released when a target is impacted by a hypervelocity particle. It is caused by emissions from a jet of shocked material which is thrown from the impact site. Impact flash phenomenology has been known for decades, and is now being considered for applications where remote diagnostics are required to observe and diagnose impacts on satellites and space craft where micrometeoroid and orbital debris impacts are common. Additionally, this phenomena and remote diagnostics are under consideration for missile defense applications. Currently, optical signatures created from hypervelocity impact can be utilized as the basis for detectors (spectrometers, pyrometers), which characterize the material composition and temperature. More recent interest has focused on study of hypervelocity impact generated debris and the physics of the associated rapidly expanding and cooling multiphase debris cloud. To establish this capability technically in the laboratory, we have conducted a series of experiments on a two-stage light gas gun at impact velocities ranging from 6 to 19 km/s, which is representative for light emissions resulting from hypervelocity impacts in space. At these high impact velocities jetting is no longer the dominant mechanism for observed impact flash signatures. The focus of this work is to develop fast, inexpensive photo-diodes for use as a reliable prompt flash, and late time radiating debris cloud diagnostic to: (a) characterize material behavior in the shocked and expanding state when feasible; (b) ascertain scaling of luminosity with impact velocity; (c) determine the temperature of the impact flash resulting from radiating emissions when multiple silicon diodes are used in conjunction with narrow band pass filtering at specific wavelengths as a pyrometer. The results of these experiments are discussed in detail using both a metallic target, such as aluminum, and an organic material such as Composition-B explosive.