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161.
Bourgois TM Nguyen DV Sansen S Rombouts S Beliën T Fierens K Raedschelders G Rabijns A Courtin CM Delcour JA Van Campenhout S Volckaert G 《Journal of biotechnology》2007,130(1):95-105
The Bacillus subtilis endoxylanase XynA (BSXY) is frequently used to improve the functionality of arabinoxylan-containing material in cereal based industries. The presence of endogenous Triticum aestivum xylanase inhibitors (TAXI-I and TAXI-II) in wheat is a real concern as they have a direct negative impact on the efficiency of this enzyme. Here, we used the recently determined structure of the complex between TAXI-I and an endoxylanase of Aspergillus niger to develop inhibitor-insensitive BSXY variants by site-directed mutagenesis of strategically chosen amino acids. We either induced steric hindrance to reject the inhibitors or interrupted key interactions with the inhibitors in the endoxylanase substrate-binding groove. The first strategy was successfully applied to position G12 where G12W combined inhibition insensitivity with unharmed catalytic performance. Variants from the second strategy showed altered inhibitor sensitivities concomitant with changes in enzyme activities and allowed to gain insight in the binding-mode of both TAXI-I and TAXI-II with BSXY. 相似文献
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Stefaan W. Verbruggen Ted J. Vaughan Laoise M. McNamara 《Biomechanics and modeling in mechanobiology》2014,13(1):85-97
Osteocytes are believed to be the primary sensor of mechanical stimuli in bone, which orchestrate osteoblasts and osteoclasts to adapt bone structure and composition to meet physiological loading demands. Experimental studies to quantify the mechanical environment surrounding bone cells are challenging, and as such, computational and theoretical approaches have modelled either the solid or fluid environment of osteocytes to predict how these cells are stimulated in vivo. Osteocytes are an elastic cellular structure that deforms in response to the external fluid flow imposed by mechanical loading. This represents a most challenging multi-physics problem in which fluid and solid domains interact, and as such, no previous study has accounted for this complex behaviour. The objective of this study is to employ fluid–structure interaction (FSI) modelling to investigate the complex mechanical environment of osteocytes in vivo. Fluorescent staining of osteocytes was performed in order to visualise their native environment and develop geometrically accurate models of the osteocyte in vivo. By simulating loading levels representative of vigorous physiological activity ( $3,000\,\upmu \upvarepsilon $ compression and 300 Pa pressure gradient), we predict average interstitial fluid velocities $(\sim 60.5\,\upmu \text{ m/s })$ and average maximum shear stresses $(\sim 11\, \text{ Pa })$ surrounding osteocytes in vivo. Interestingly, these values occur in the canaliculi around the osteocyte cell processes and are within the range of stimuli known to stimulate osteogenic responses by osteoblastic cells in vitro. Significantly our results suggest that the greatest mechanical stimulation of the osteocyte occurs in the cell processes, which, cell culture studies have indicated, is the most mechanosensitive area of the cell. These are the first computational FSI models to simulate the complex multi-physics mechanical environment of osteocyte in vivo and provide a deeper understanding of bone mechanobiology. 相似文献
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Van Onckelen Henri; Rudelsheim Patrick; Hermans Robert; Horemans Stefaan; Messens Eric; Hernalsteens Jean-Pierre; van Montagu Marc; De Greef Jan 《Plant & cell physiology》1984,25(6):1017-1025
The kinetics of endogenous cytokinin, IAA and ABA levels duringthe growth cycle of a wild-type tobacco crown gall (W38-B6S3)were compared with that of a shoot-inducing (Shi-) mutant. Inboth tumor types, high IAA and cytokinin (essentially ribosyl-trans-zeatinand its corresponding glucoside) levels were built up by theend of the linear growth phase and maintained during the greaterpart of the exponential growth period. The stationary phasewas preceded by a very drastic decrease in the endogenous levelof both hormones. Quantitatively, the wild-type tumour showed a higher IAA leveland a reduced cytokinin level compared with the Shi- mutant.No significantly different endogenous ABA pattern was observed.The reduced cytokinin level might correspond to the ratio oftransformed/untransformed cells in the wild-type tumour whereasthe reduced IAA level in the Shi- mutant may be correlated withthe deletion of gene 2 in the T-DNA of the pGV 2206 Ti plasmid. The elevated cytokinin/IAA ratio induced shooting mainly ofthe untransformed cells in the Shi- mutant tissue whereas inthe wild-type, the shoot suppression was compatible with thereduced cytokinin/IAA ratio.
4Senior Research Associate Nationaal Fonds WetenschappelijkOnderzoek (N.F.W.O.).
5Research Associate N.F.W.O.
6Recipient of an Instituut voor Wetenschappelijk Onderzoek inNijverheid en Landbouw grant. (Received February 23, 1984; Accepted June 19, 1984) 相似文献
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A new formula for the statistical uncertainty of “loss-free counting” (LFC) is presented. Its validity is demonstrated by
comparing with experimental data obtained with a HPGe γ-ray spectrometer. Also, computer simulation data of nuclear counting
with different types of count loss (pileup rejection, extending and nonextending dead time) are in agreement with the predicted
counting uncertainty. The proposed formula for LFC uncertainty is applicable to spectrometers with a classical semi-Gaussian
pulse-shaping amplifier as well as with a gated-integrator amplifier. Hence, achieving statistical control seems to be a feasible
goal. 相似文献
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Kris Gevaert Hans De Mol Jean-Luc Verschelde Jozef Van Damme Stefaan De Boeck Joël Vandekerckhove 《Journal of Protein Chemistry》1997,16(5):335-342
A combination of techniques is presented allowing gel-purified protein identification in the femtomole range using matrix-assisted-laser-desorption-ionization mass spectrometry. The proteins are detected in the primary gel by a sensitive negative staining procedure, transferred, and concentrated in a secondary gel matrix. There, they are digested in the presence of H2
18O and their sequences are predicted (1) by peptide mass fingerprinting, (2) by comparing the post-source-decay (PSD) spectra with theoretical spectra of candidate isobaric peptides using a computer algorithm called MassFrag, and (3) by a manual readout of the 18O/16O-labeled fragmentation ions in the PSD spectra. 相似文献
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