871 research outputs found

    Effect of Maillard induced glycation on protein hydrolysis by lysine/arginine and non-lysine/arginine specific proteases

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    Enzymatic protein hydrolysis is sensitive to modifications of protein structure, e.g. Maillard reaction. In early stages of the reaction glycation takes place, modifying the protein primary structure. In later stages protein aggregation occurs. The specific effect of glycation on protein hydrolysis was studied using α-lactalbumin glycated with D-glucose at 50 °C (0–10 h). This resulted in proteins with different degrees of glycation (DG = 0–63%) without changes in secondary, tertiary and quaternary structure. These glycated proteins were hydrolyzed by lysine/arginine specific proteases (bovine and porcine trypsin) or by non-lysine/arginine specific proteases (Bacillus licheniformis protease (BLP), α-chymotrypsin and subtilisin A). For bovine and porcine trypsin, the maximal degree of hydrolysis decreased linearly with 65% from untreated to maximal glycated protein (DG = 63%). This means trypsin cannot hydrolyze glycated cleavage sites. BLP and subtilisin A hydrolyses were independent of glycation, while α-chymotrypsin cannot hydrolyze cleavage sites with glycated binding sites. This means for non-lysine/arginine specific proteases, the effect of glycation depends on the enzyme sensitivity towards modifications on binding sites. Since not all cleavage sites are efficiently used by the enzymes, the extent of the effects depends on the enzyme selectivity towards cleavage sites (for trypsin) or cleavage sites near glycation sites (for α-chymotrypsin). Combining the results of all proteases, an equation was derived describing the effect of modification of protein primary structure on the extent of hydrolysis based on the enzyme specificity, selectivity and binding site sensitivity

    De geneesmiddelenmarkt in observatie

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    Er wordt veel geld uitgegeven aan medicijnen. In 1985 verstrekten apothekers en huisartsen voor ongeveer f. 3 mrd. (incl. honorarium) aan geneesmiddelen. Deze uitgaven zijn in de periode 1980-1985 fors toegenomen. Bovendien zijn geneesmiddelen in alle EGlanden, uitgezonderd West-Duitsland, aanmerkelijk goedkoper dan in ons land. In dit artikel wordt de Nederlandse geneesmiddelenmarkt onder de loep genomen. De auteurs constateren dat er bij zowel de verstrekkers als de gebruikers van medicijnen onvoldoende prikkels aanwezig zijn tot kostenbeheersing. De auteurs hebben hiervoor een aantal suggesties in petto

    Electronic Theory for the Nonlinear Magneto-Optical Response of Transition-Metals at Surfaces and Interfaces: Dependence of the Kerr-Rotation on Polarization and on the Magnetic Easy Axis

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    We extend our previous study of the polarization dependence of the nonlinear optical response to the case of magnetic surfaces and buried magnetic interfaces. We calculate for the longitudinal and polar configuration the nonlinear magneto-optical Kerr rotation angle. In particular, we show which tensor elements of the susceptibilities are involved in the enhancement of the Kerr rotation in nonlinear optics for different configurations and we demonstrate by a detailed analysis how the direction of the magnetization and thus the easy axis at surfaces and buried interfaces can be determined from the polarization dependence of the nonlinear magneto-optical response, since the nonlinear Kerr rotation is sensitive to the electromagnetic field components instead of merely the intensities. We also prove from the microscopic treatment of spin-orbit coupling that there is an intrinsic phase difference of 90∘^{\circ } between tensor elements which are even or odd under magnetization reversal in contrast to linear magneto-optics. Finally, we compare our results with several experiments on Co/Cu films and on Co/Au and Fe/Cr multilayers. We conclude that the nonlinear magneto-optical Kerr-effect determines uniquely the magnetic structure and in particular the magnetic easy axis in films and at multilayer interfaces.Comment: 23 pages Revtex, preprintstyle, 2 uuencoded figure

    Highly site-specific H2 adsorption on vicinal Si(001) surfaces

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    Experimental and theoretical results for the dissociative adsorption of H_2 on vicinal Si(001) surfaces are presented. Using optical second-harmonic generation, sticking probabilities at the step sites are found to exceed those on the terraces by up to six orders of magnitude. Density functional theory calculations indicate the presence of direct adsorption pathways for monohydride formation but with a dramatically lowered barrier for step adsorption due to an efficient rehybridization of dangling orbitals.Comment: 5 pages, 4 figures, submitted to Phys. Rev. Lett. (1998). Other related publications can be found at http://www.fhi-berlin.mpg.de/th/paper.htm

    Interactive effects of vascular risk burden and advanced age on cerebral blood flow.

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    Vascular risk factors and cerebral blood flow (CBF) reduction have been linked to increased risk of cognitive impairment and Alzheimer's disease (AD); however the possible moderating effects of age and vascular risk burden on CBF in late life remain understudied. We examined the relationships among elevated vascular risk burden, age, CBF, and cognition. Seventy-one non-demented older adults completed an arterial spin labeling MR scan, neuropsychological assessment, and medical history interview. Relationships among vascular risk burden, age, and CBF were examined in a priori regions of interest (ROIs) previously implicated in aging and AD. Interaction effects indicated that, among older adults with elevated vascular risk burden (i.e., multiple vascular risk factors), advancing age was significantly associated with reduced cortical CBF whereas there was no such relationship for those with low vascular risk burden (i.e., no or one vascular risk factor). This pattern was observed in cortical ROIs including medial temporal (hippocampus, parahippocampal gyrus, uncus), inferior parietal (supramarginal gyrus, inferior parietal lobule, angular gyrus), and frontal (anterior cingulate, middle frontal gyrus, medial frontal gyrus) cortices. Furthermore, among those with elevated vascular risk, reduced CBF was associated with poorer cognitive performance. Such findings suggest that older adults with elevated vascular risk burden may be particularly vulnerable to cognitive change as a function of CBF reductions. Findings support the use of CBF as a potential biomarker in preclinical AD and suggest that vascular risk burden and regionally-specific CBF changes may contribute to differential age-related cognitive declines

    Theory for Spin-Polarized Oscillations in Nonlinear Magneto-Optics due to Quantum Well States

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    Using an electronic tight-binding theory we calculate the nonlinear magneto-optical response from an x-Cu/1Fe/Cu(001) film as a function of frequency and Cu overlayer thickness (x=3 ... 25). We find very strong spin-polarized quantum well oscillations in the nonlinear magneto-optical Kerr effect (NOLIMOKE). These are enhanced by the large density of Fe dd states close to the Fermi level acting as intermediate states for frequency doubling. In good agreement with experiment we find two oscillation periods of 6-7 and 11 monolayers the latter being more pronounced.Comment: 12 pages, Revtex, 3 postscript figure

    Nonlinear Magneto-Optical Response of ss- and dd-Wave Superconductors

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    The nonlinear magneto-optical response of ss- and dd-wave superconductors is discussed. We carry out the symmetry analysis of the nonlinear magneto-optical susceptibility in the superconducting state. Due to the surface sensitivity of the nonlinear optical response for systems with bulk inversion symmetry, we perform a group theoretical classification of the superconducting order parameter close to a surface. For the first time, the mixing of singlet and triplet pairing states induced by spin-orbit coupling is systematically taken into account. We show that the interference of singlet and triplet pairing states leads to an observable contribution of the nonlinear magneto-optical Kerr effect. This effect is not only sensitive to the anisotropy of the gap function but also to the symmetry itself. In view of the current discussion of the order parameter symmetry of High-Tc_c superconductors, results for a tetragonal system with bulk singlet pairing for various pairing symmetries are discussed.Comment: 21 pages (REVTeX) with 8 figures (Postscript
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