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811.
Anton Slavov Catherine Garnier Marie-Jeanne Crpeau Sylvie Durand Jean-Franois Thibault Estelle Bonnin 《Carbohydrate polymers》2009,77(4):876-884
High methoxy pectin was submitted to various amounts of a fungal pectin methylesterase (PME) from Aspergillus aculeatus and of a plant PME from orange in the presence of calcium. The systems were characterized by rheological means during the gelation process. By the way of in situ demethoxylation with low amount of orange PME, it was possible to gel pectin from the beginning of the reaction although its high degree of methylation around 70. To understand this unusual properties, the behaviour of the two enzymes was investigated in pectic gels and in solution through the analysis of content and distribution of the remaining methyl esters. In the gel, the degree of methylation decreased slowly with orange PME and rapidly with Aspergillus PME. The degree of methylation and degree of blockiness after treatment with each PME in solution or in gels were slightly different. Possible explanations for this are evolving visco-elastic properties, including gel formation or influence of calcium on the enzyme–substrate complex. 相似文献
812.
Schirer Alicia Rouch Anne Marcheteau Estelle Stojko Johann Sophie Landron Jeantet Elodie Fould Benjamin Ferry Gilles Boutin Jean A. 《Molecular biology reports》2022,49(1):149-161
Molecular Biology Reports - Posttranslational modifications of proteins are catalyzed by a large family of enzymes catalyzing many chemical modifications. One can hijack the natural use of those... 相似文献
813.
814.
Zhiguang Xiao Andrew R. Gardner Maddalena Cross Estelle M. Maes Roman S. Czernuszewicz Marco Sola Anthony G. Wedd 《Journal of biological inorganic chemistry》2001,6(5-6):638-649
Redox thermodynamic data provide a detailed insight into control of the reduction potential E degrees' of the [Fe(S-Cys)4] site in rubredoxin. Mutant forms were studied in which specific structural changes were made in both the primary and secondary coordination spheres. Those changes have been probed by resonance Raman spectroscopy. The decrease of approximately 200 mV in E degrees' observed for the [Fe(S-Cys)3(O-Ser)]-/2- couples in the surface ligand mutants C9S and C42S is essentially enthalpic in origin and associated with the substitution of ligand thiolate by ligand olate. However, the pH dependence of the potentials below characteristic pKa(red) approximately equals 7 is an entropic contribution, plausibly associated with increased conformational flexibility induced by a longer Fe(II)-O(H)-Ser bond in the reduced form. The presence of a second surface Ser ligand in the new double mutant protein C9S/C42S affects the enthalpic term primarily for pH>pKa(red) > or = 9.3, but for pHpKa approximately 9: [Fe(III)(S-Cys)3(OH)]- + e- --> [Fe(II)(S-Cys)3(OH)]2-. pH [Fe(II)(S-Cys)3(OH2)]-. 相似文献
815.
Yolande Bertin J. P. Girardeau F. Chaucheyras‐Durand Bernard Lyan Estelle Pujos‐Guillot Josée Harel Christine Martin 《Environmental microbiology》2011,13(2):365-377
The bovine gastrointestinal tract is the main reservoir for enterohaemorrhagic Escherichia coli (EHEC) responsible for food‐borne infections. Characterization of nutrients that promote the carriage of these pathogens by the ruminant would help to develop ecological strategies to reduce their survival in the bovine gastrointestinal tract. In this study, we show for the first time that free ethanolamine (EA) constitutes a nitrogen source for the O157:H7 EHEC strain EDL933 in the bovine intestinal content because of induction of the eut (ethanolamine utilization) gene cluster. In contrast, the eut gene cluster is absent in the genome of most species constituting the mammalian gut microbiota. Furthermore, the eutB gene (encoding a subunit of the enzyme that catalyses the release of ammonia from EA) is poorly expressed in non‐pathogenic E. coli. Accordingly, EA is consumed by EHEC but is poorly metabolized by endogenous microbiota of the bovine small intestine, including commensal E. coli. Interestingly, the capacity to utilize EA as a nitrogen source confers a growth advantage to E. coli O157:H7 when the bacteria enter the stationary growth phase. These data demonstrate that EHEC strains take advantage of a nitrogen source that is not consumed by the resident microbiota, and suggest that EA represents an ecological niche favouring EHEC persistence in the bovine intestine. 相似文献
816.
We modified a video digitizer system to allow short-term high-resolution measurements of root elongation in intact seedlings ofArabidopsis thaliana (L.) Heynh. We used the system to measure the kinetics of promotion and inhibition of root elongation by applied auxin and to determine the dose-response relationship for auxin action on elongation in roots of wild-type seedlings and seedlings of mutants (axr1,aux1, andaxr2) with altered auxin responsiveness. Roots of the mutants showed less inhibition in the presence of inhibitory concentrations of auxin than did roots of the wild type. The latent period preceding the change in elongation rate after auxin application was the same foraxr1 andaxr2 as for the wild type whereas the latent period foraux1 was about twice as long as for the wild type. Low concentrations (ca. 10–11 M) of auxin induced substantial promotion of root elongation in the wild type and inaxr2.We thank Linda Young and Roger Hangarter for helping to develop the system for mountingArabidopsis seedlings and Wendy Hankie, Julia Hufford, and Ruperto Villella for doing some of the experiments. We thank Roger Hangarter for valuable discussions of the data. This work was supported by National Science Foundation Grant No. DCB-9105807 and by National Aeronautics and Space Administration Grant No. NAG10-0084 相似文献
817.
Crowing behavior was monitored constantly in male Japanese quail housed singly over 30 successive days. The photoperiod was 16h of light and 8 h of dark. A daily pattern in crowing was observed in which the frequencies were elevated in the afternoon and at the beginning of darkness. However, peak crowing occured 2 h prior to the onset of light. These rhythms were highly correlated among individuals and extremely repeatable over the sequential days of observation.In a second experiment, males which were paired with females were observed for frequencies of crowing, courtship, and mating behavior during the lighted portion of the day. In this experiment, the same photoperiod (16L:8D) was maintained. Paired males exhibited a daily pattern in crowing similar to that observed in the singly housed males. The frequency of mating was the highest between 1200 and 1300 h and lowest at 1400 h. Mating success was highest at midday, as were the number of males exhibiting mating behavior. These diurnal patterns in sexual behavior may depend on environmental cues such as photoperiod, which, in turn, may stimulate endocrine triggers. 相似文献
818.
F Estelle R Simons 《BMJ (Clinical research ed.)》2008,336(7654):1141-1142
819.
Phagocytosis in adherent P388D1 (D1) cells was monitored utilizing formalin treated () previously labeled with 125iododeoxyuridine. The dependence of this phagocytic process on calcium was studied by using several agents which alter calcium metabolism. The calcium antagonist ruthenium red (RR) produced a dose and time dependent stimulation (60–70%) of phagocytosis by D1 cells. Utilizing another calcium antagonist, D-600, a prolonged inhibition (4 hours) of phagocytosis (40%) was observed. The addition of the cation ionophore A23187 produced a transient stimulatory increase (38% at 2 hours) in the phagocytic response. The concomitant addition of RR and D-600 did not alter the phagocytosis of by D1 cells as compared to control cells. However, this complete drug/drug antagonism was not seen with the combinations of A23187 and D-600 or RR and A23187. The addition of A23187 and D-600 resulted in a time dependent inhibition of phagocytosis which did not become maximal until 3 to 4 hours. A23187 and RR produced a time independent stimulation of phagocytosis which was significantly less than that which was observed for RR alone, but was of longer duration than the response produced by A23187 alone. The use of these calcium probes in the P388D1 macrophage model suggests a role for calcium in the phagocytic process. 相似文献
820.