Interest in protease inhibitors has been renewed because of their potent activity in preventing carcinogenesis in a wide variety of in vivo and in vitro model systems. Potato tubers contain a wide... Show moreInterest in protease inhibitors has been renewed because of their potent activity in preventing carcinogenesis in a wide variety of in vivo and in vitro model systems. Potato tubers contain a wide range of such protease inhibitors. In cv. Elkana potato tubers, protease inhibitors represent about 50% of the total amount of soluble protein. Potato serine protease inhibitor (PSPI), one of the isoforms of the most abundant group of protease inhibitors, is a dimeric double-headed Kunitz-type inhibitor. No high-resolution structural information on this type of inhibitor has so far been obtained, as all currently known structures are of the monomeric single-headed or monomeric double-headed types. Crystals were grown in 0.1 M HEPES pH 7.5, 10% PEG 8000 and 8% ethylene glycol complemented with 9 mM 1-s-octyl-beta-D-thioglucoside or 0.1 M glycine. Data were collected from a single crystal under cryoconditions to 1.8 Angstrom resolution. The protein crystallized in space group P2(1), with unit-cell parameters a = 54.82, b = 93.92, c = 55.44 Angstrom, beta = 100.7degrees; the scaling R-sym is 0.044 for 45 456 unique reflections. Show less
Ratnala, V.R.P.; Swarts, H.G.P.; Oostrum, J. van; Leurs, R.; Groot, H.J.M. de; Bakker, R.A.; Grip, W.J. de 2004
The copper-containing nitrite reductase from Alcaligenes faecalis S-6 was found to catalyze the oxidation of nitric oxide to nitrite, the reverse of its physiological reaction. Thermodynamic and... Show moreThe copper-containing nitrite reductase from Alcaligenes faecalis S-6 was found to catalyze the oxidation of nitric oxide to nitrite, the reverse of its physiological reaction. Thermodynamic and kinetic constants with the physiological electron donor pseudoazurin were determined for both directions of the catalyzed reaction in the pH range of 6-8. For this, nitric oxide was monitored by a Clark-type electrode, and the redox state of pseudoazurin was measured by optical spectroscopy. The equilibrium constant (K-eq) depends on the reduction potentials of pseudoazurin and nitrite/nitric oxide, both of which vary with pH. Above pH 6.2 the formation of NiR substrates (nitrite and reduced pseudoazurin) is favored over the products (NO and oxidized pseudoazurin). At pH 8 the K-eq amounts to 103. The results show that dissimilatory nitrite reductases catalyze an unfavorable reaction at physiological pH (pH = 7-8). Consequently, nitrous oxide production by copper-containing nitrite reductases is unlikely to occur in vivo with a native electron donor. With increasing pH, the rate and specificity constant of the forward reaction decrease and become lower than the rate of the reverse reaction. The opposite occurs for the rate of the reverse reaction; thus the catalytic bias for nitrite reduction decreases. At pH 6.0 the kat for nitrite reduction was determined to be 1.5 x 10(3) s(-1), and at pH 8 the rate of the reverse reaction is 125 s(-1). Show less
The influence of peptide-protein interactions on the electrochemistry of copper-containing pseudoazurin from Alcaligenes faecalis strain S-6 has been investigated by covalently binding cysteine... Show moreThe influence of peptide-protein interactions on the electrochemistry of copper-containing pseudoazurin from Alcaligenes faecalis strain S-6 has been investigated by covalently binding cysteine-containing hexapeptides to a gold electrode surface. The hexapeptides contain three cysteines in the same positions with the remaining amino acids varied to give mixed charge (lysine, threonine, alanine), positive (lysine), overall neutral (alanine), and negative (glutamate) chemically modified electrode surfaces. These systematic variations in the amino acid sequence lead to large variations in voltammetric behavior for the Cu(II) --> Cu(I) heterogeneous pseudoazurin redox process encompassing fully reversible and diffusional, transitionally adsorbed, or strongly adsorbed forms of voltammetry. The variations in voltammetric behavior may be related to electrostatic interactions between the charges from the hexapeptide electrode modifiers and surface charges of pseudoazurin. A possible description of the pseudoazurin-electrode surface interaction is given. Show less
The Milky Way is the cornerstone of our understanding of galaxies. The structureand kinematics of its gas and stars can be studied in unique detail due totheir relative proximity. However, being... Show moreThe Milky Way is the cornerstone of our understanding of galaxies. The structureand kinematics of its gas and stars can be studied in unique detail due totheir relative proximity. However, being located well within the Galactic diskand thereby observing the Milky Way in nonlinear projection makes it difcultto properly map its large-scale morphology.One of the interesting ndings has been that observations of molecular lineemission (CO, HI) and stellar motions show signatures of a Galactic Bar in the innerGalaxy. However, its characteristics such as elongation, thickness and viewingangle are still poorly constrained. One of the main obstacles has been thestrong obscuration by interstellar dust toward the inner Galaxy, which makesoptical studies of the stellar population in that region almost impossible. Theextinction is less severe at near- and mid-infrared wavelengths. To characterisethe structure and formation history of the Milky Way, several infrared surveyswere conducted during the past decade: ISOGAL, MSX, DENIS, 2MASS. Thesedata contain a wealth of information on the structure of the stellar populationsthat has yet to be fully analysed. Having entered a golden age for Galactic astronomy,soon even more detailed imaging and spectroscopy will be provided bythe Spitzer Space Telescope, while the GAIA satellite will provide unprecedentedastrometry.My thesis research has focused on the structure and stellar population of theinner 4 kpc of the Milky Way. I have analysed data from recent infrared surveysand obtained SiO radio maser line observations of late-type giants to study thestar formation history and the gravitational potential of the inner Galaxy. Withages ranging from less than 1 to 15 Gyr, the infrared-luminous late-type giantstars are representative of the bulk of the Galactic stellar population, and hencetrace its star formation history. Their spatial abundance variation maps the stellarmass distribution, and thereby probes the Galactic gravitational potential. Thereddening of their spectral energy distribution can be used to map the interstellarextinction. Their envelopes often emit strong molecular masers (OH, SiO) thatcan be detected throughout the Galaxy, and through the precise measurement ofthe maser line velocity they reveal the stars' line-of-sight velocities. Thereforethey are ideal tracers of the Galactic kinematics and gravitational potential. Show less
Bordered pits play an important role in permitting water flow among adjacent tracheary elements in flowering plants. Variation in the bordered pit structure is suggested to be adaptive in optimally... Show moreBordered pits play an important role in permitting water flow among adjacent tracheary elements in flowering plants. Variation in the bordered pit structure is suggested to be adaptive in optimally balancing the conflict between hydraulic efficiency (conductivity) and safety from air entry at the pit membrane (air seeding). The possible function of vestured pits, which are bordered pits with protuberances from the secondary cell wall of the pit chamber, could be increased hydraulic resistance or minimized vulnerability to air seeding. These functional hypotheses have to be harmonized with the notion that the vestured or nonvestured nature of pits contains strong phylogenetic signals (i.e., often characterize large species-rich clades with broad ecological ranges). A literature survey of 11,843 species covering 6,428 genera from diverse climates indicates that the incidence of vestured pits considerably decreases from tropics to tundra. The highest frequencies of vestured pits occur in deserts and tropical seasonal woodlands. Moreover, a distinctly developed network of branched vestures is mainly restricted to warm habitats in both mesic and dry (sub)tropical lowlands, whereas vestures in woody plants from cold and boreal arctic environments are usually minute and simple. A similar survey of the frequency of exclusively scalariform perforation plates illustrates that the major ecological trend of this feature is opposite that of vestured pits. These findings provide previously undescribed insights suggesting that vessels with vestured pits and simple perforation plates function as an efficient hydraulic system in plants growing in warm environments with periodical or continuous drought stress. Show less
The serine protease inhibitor C1-Inhibitor (C1-Inh) inhibits several complement- and contact-system proteases, which play an important role in inflammation. C1-Inh has a short reactive site loop ... Show moreThe serine protease inhibitor C1-Inhibitor (C1-Inh) inhibits several complement- and contact-system proteases, which play an important role in inflammation. C1-Inh has a short reactive site loop (RSL) compared to other serpins. RSL length determines the inhibitory activity of serpins. We investigated the effect of RSL elongation on inhibitory activity of C1-Inh by insertion of one or two alanine residues in the RSL. One of five mutants had an increased association rate with kallikrein, but was nevertheless a poor inhibitor because of a simultaneous high stoichiometry of inhibition (>10). The association rate of the other variants was lower than that of wild-type C1-Inh. These data suggest that the relatively weak inhibitory activity of C1-Inh is not the result of its short RSL. The short RSL of C1-Inh has, surprisingly, the optimal length for inhibition. (C) 2004 Elsevier B.V. All rights reserved. Show less
Tijdens de algemene ledenvergadering van 6 april 2004 werd Sander Dekker uitgeroepen tot Lid van Verdienste, vanwege zijn jarenlange inzet voor de vereniging. Zo was hij medeoprichter van het ICR ... Show moreTijdens de algemene ledenvergadering van 6 april 2004 werd Sander Dekker uitgeroepen tot Lid van Verdienste, vanwege zijn jarenlange inzet voor de vereniging. Zo was hij medeoprichter van het ICR (International Contract Research) red. , bestuursvoorzitter en was hij lid van de RvA (Raad van Advies) red .. Reden genoeg voor een interview, dacht de redactie van de BB. Show less
Rosenthal e.a. leggen in het introductie boek voor bestuurskundigen Ope� baar bestuur; beleid, organisatie en politiek al jaren aan propedeusestudente _ n u� t dat 'wij spreken van een... Show moreRosenthal e.a. leggen in het introductie boek voor bestuurskundigen Ope� baar bestuur; beleid, organisatie en politiek al jaren aan propedeusestudente _ n u� t dat 'wij spreken van een zelfstandig bestuursorgaan wanneer een orgamsahe na verzelfstandiging publieke taken en bevoegdheden behoudt en een publiekrechtelijke rechtsvorm krijgt (uitzonderingen daargelaten). Er is in dit geval geen directe hiërarchische ondergeschiktheid aan de minister meer'.1 Deze passage is zeer waarschijnlijk braaf onderstreept door het merendeel van de studenten om terug te lezen in voorbereiding op het tentamen Bestuurskunde 1. Show less
Tijden van optimisme zijn voorbij; infectieziekten1 zijn alles behalve overwonnen. SARS vormde wat dat betreft vrij recentelijk een wake-up call voor de wereld; binnen enkele maanden verspreidde de... Show moreTijden van optimisme zijn voorbij; infectieziekten1 zijn alles behalve overwonnen. SARS vormde wat dat betreft vrij recentelijk een wake-up call voor de wereld; binnen enkele maanden verspreidde de ziekte zich over 32 landen. Enkele decennia geleden verkeerde men in de veronderstelling dat infectieziekten misschien nog wel lastig waren, maar dat de medische wetenschap de juiste instrumenten in handen had om de microbiologische ziekteverwekkers voorgoed de baas te kunnen. Dit optimisme vond zijn oorsprong in de ontwikkeling van vaccins en antibiotica waardoor ziekten beter te bestrijden waren, de uitvinding van de elektronenmicroscoop, en de wereldwijde eradicatie van het pokkenvirus2 • Show less
