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101.
Physical gelation of chitosan in the presence of beta-glycerophosphate: the effect of temperature 总被引:2,自引:0,他引:2
When adding beta-glycerophosphate (beta-GP), a weak base, to chitosan aqueous solutions, the polymer remains in solution at neutral pH and room temperature, while homogeneous gelation of this system can be triggered upon heating. It is therefore one of the rare true physical chitosan hydrogels. In this study, physicochemical and rheological properties of chitosan solutions in the presence of acetic acid and beta-GP were investigated as a function of temperature in order to gain a better understanding of the gelation mechanisms. The gel structure formed at high temperature was only partially thermoreversible upon cooling to 5 degrees C because of the existence of remaining associations, confirmed by the spontaneous recovery of the gel after breakup at low temperature. Increasing temperature had no effect on the pH values of this system, while conductivity (and calculated ionic strength) increased. Values from the pH measurements were used to estimate the degree of protonation of each species as a function of temperature. The decreasing ratio of -NH3+ in chitosan and -OPO(O-)2 in beta-GP suggested reduced chitosan solubility along with a diminution of ionic interactions such as ionic bridging with increasing temperature. On the other hand, the increased ionic strength as a function of temperature, in the presence of beta-GP, enhanced screening of electrostatic repulsion and increased hydrophobic effect, resulting in favorable conditions for gel formation. Therefore, our study suggests that hydrophobic interactions and reduced solubility are the main driving force for chitosan gelation at high temperature in the presence of beta-GP. 相似文献
102.
Lancelot N Charier G Couprie J Duband-Goulet I Alpha-Bazin B Quémeneur E Ma E Marsolier-Kergoat MC Ropars V Charbonnier JB Miron S Craescu CT Callebaut I Gilquin B Zinn-Justin S 《Nucleic acids research》2007,35(17):5898-5912
DNA damage checkpoints are signal transduction pathways that are activated after genotoxic insults to protect genomic integrity. At the site of DNA damage, ‘mediator’ proteins are in charge of recruiting ‘signal transducers’ to molecules ‘sensing’ the damage. Budding yeast Rad9, fission yeast Crb2 and metazoan 53BP1 are presented as mediators involved in the activation of checkpoint kinases. Here we show that, despite low sequence conservation, Rad9 exhibits a tandem tudor domain structurally close to those found in human/mouse 53BP1 and fission yeast Crb2. Moreover, this region is important for the resistance of Saccharomyces cerevisiae to different genotoxic stresses. It does not mediate direct binding to a histone H3 peptide dimethylated on K79, nor to a histone H4 peptide dimethylated on lysine 20, as was demonstrated for 53BP1. However, the tandem tudor region of Rad9 directly interacts with single-stranded DNA and double-stranded DNAs of various lengths and sequences through a positively charged region absent from 53BP1 and Crb2 but present in several yeast Rad9 homologs. Our results argue that the tandem tudor domains of Rad9, Crb2 and 53BP1 mediate chromatin binding next to double-strand breaks. However, their modes of chromatin recognition are different, suggesting that the corresponding interactions are differently regulated. 相似文献
103.
O'Donnell L Panier S Wildenhain J Tkach JM Al-Hakim A Landry MC Escribano-Diaz C Szilard RK Young JT Munro M Canny MD Kolas NK Zhang W Harding SM Ylanko J Mendez M Mullin M Sun T Habermann B Datti A Bristow RG Gingras AC Tyers MD Brown GW Durocher D 《Molecular cell》2010,40(4):619-631
Genome integrity is jeopardized each time DNA replication forks stall or collapse. Here we report the identification of a complex composed of MMS22L (C6ORF167) and TONSL (NFKBIL2) that participates in the recovery from replication stress. MMS22L and TONSL are homologous to yeast Mms22 and plant Tonsoku/Brushy1, respectively. MMS22L-TONSL accumulates at regions of ssDNA associated with distressed replication forks or at processed DNA breaks, and its depletion results in high levels of endogenous DNA double-strand breaks caused by an inability to complete DNA synthesis after replication fork collapse. Moreover, cells depleted of MMS22L are highly sensitive to camptothecin,?a topoisomerase I poison that impairs DNA replication progression. Finally, MMS22L and TONSL are necessary for the efficient formation of RAD51 foci after DNA damage, and their depletion impairs homologous recombination. These results indicate that MMS22L and TONSL are genome caretakers that stimulate the recombination-dependent repair of stalled or collapsed replication forks. 相似文献
104.
105.
Christelle David Laurent Bischoff Hervé Meudal Catherine Llorens-Cortes Bernard Pierre Roques Marie-Claude Fournié-Zaluski 《International journal of peptide research and therapeutics》1997,4(4-6):411-414
Summary In order to study the physiological role of aminopeptidase A(APA), several α-mercapto-β-amino acyl dipeptides were synthesized
to obtain compounds having a high affinity for APA and a high selectivity versus aminopeptidase N (APN). Sulfornamide and
carboxylate moieties which have been shown to be recognized by the S1 subsite of the enzyme were introduced on the side chain of the α-mercapto-β-amino acyl sub-unit, the latter being coupled
to dipeptides optimized to interact with the S'1 and S'2 subsites by means of combinatorial chemistry. Good affinities (16nM) were obtained, the selectivity factors being up to 160-fold
versus APN. 相似文献
106.
Aurélie Albert Marie-Claude Huynen Tommaso Savini Alain Hambuckers 《International journal of primatology》2013,34(4):696-713
Food availability may influence primates’ home range size and use. Understanding this relationship may facilitate the design of conservation strategies. We aimed to determine how fruit availability influences the ranging patterns of a group of northern pig-tailed macaques (Macaca leonina) living around the visitor center of Khao Yai National Park, Thailand. We predicted that macaques would increase their range during low fruit abundance periods to gather high-quality food and that they would go where there are more fruits or more fruits of particular species. We also predicted that human food, linked to human presence, would attract the macaques. We followed the macaques and recorded their diet and movements within their home range. We superimposed a grid on kernels defining the monthly home range surface to compare spatially macaques’ travel and the availability of fruits measured on botanical transects. Our results showed that the macaques increased their monthly home range in March, probably to obtain newly available fruits. During high fruit abundance seasons, they spent more time near particular fruit species. In August and September, although fruits became rare again, macaques kept their home range large, perhaps to find enough fruits as supplies dwindled. Finally, from October to February, they decreased their monthly home range size while consuming human food, a high-quality item. In conclusion, the macaques used several ranging strategies according to fruit availability. However, we think that, without human food, macaques would tend to increase their range during low fruit abundance periods, as predicted. 相似文献
107.
Shlomit Jacobson-Pick Marie-Claude Audet Robyn Jane McQuaid Rahul Kalvapalle Hymie Anisman 《PloS one》2013,8(4)
Stressful events promote several neuroendocrine and neurotransmitter changes that might contribute to the provocation of psychological and physical pathologies. Perhaps, because of its apparent ecological validity and its simple application, there has been increasing use of social defeat (resident-intruder) paradigms as a stressor. The frequency of stress-related psychopathology is much greater in females than in males, but the typical resident-intruder paradigm is less useful in assessing stressor effects in females. An alternative, but infrequently used procedure in females involves exposing a mouse to a lactating dam, resulting in threatening gestures being expressed by the resident. In the present investigation we demonstrated the utility of this paradigm, showing that the standard resident-intruder paradigm in males and the modified version in females promoted elevated anxiety in a plus-maze test. The behavioral effects that reflected anxiety were more pronounced 2 weeks after the stressor treatment than they were 2 hr afterward, possibly reflecting the abatement of the stress-related of hyper-arousal. These treatments, like a stressor comprising physical restraint, increased plasma corticosterone and elicited variations of norepinephrine and serotonin levels and turnover within the prefrontal cortex, hippocampus and central amygdala. Moreover, the stressor effects were exaggerated among mice that had been exposed to a chronic or subchronic-intermittent regimen of unpredictable stressors. Indeed, some of the monoamine changes were more pronounced in females than in males, although it is less certain whether this represented compensatory changes to deal with chronic stressors that could result in excessive strain on biological systems (allostatic overload). 相似文献
108.
Hervé Poras Rémi Patouret Simon Leiris Tanja Ouimet Marie-Claude Fournié-Zaluski Bernard P. Roques 《Bioorganic & medicinal chemistry letters》2017,27(16):3883-3890
New neprilysin inhibitors containing an α-mercaptoketone HSC(R1R2)CO group, as zinc ligand were designed. Two parameters were explored for potency optimization: the size of the inhibitor which could interact with the S1, S1′ or S2′ domain of the enzyme and the nature of the substituents R1, R2 of the mercaptoketone group. Introduction of a cyclohexyl chain in R1, R2 position and a (3-thiophen)benzyl group in position R3 (compound 12n) yielded to the most potent inhibitor of this series with a Ki value of 2 ± 0.3 nM. This result suggests that this new inhibitor interacts within the S1, S1′ domain of NEP allowing a pentacoordination of the catalytic Zn2+ ion by the mercaptoketone moiety. 相似文献
109.
Fany Brotcorne Gwennan Giraud Noëlle Gunst Agustín Fuentes I. Nengah Wandia Roseline C. Beudels-Jamar Pascal Poncin Marie-Claude Huynen Jean-Baptiste Leca 《Primates; journal of primatology》2017,58(4):505-516
Robbing and bartering (RB) is a behavioral practice anecdotally reported in free-ranging commensal macaques. It usually occurs in two steps: after taking inedible objects (e.g., glasses) from humans, the macaques appear to use them as tokens, returning them to humans in exchange for food. While extensively studied in captivity, our research is the first to investigate the object/food exchange between humans and primates in a natural setting. During a 4-month study in 2010, we used both focal and event sampling to record 201 RB events in a population of long-tailed macaques (Macaca fascicularis), including four neighboring groups ranging freely around Uluwatu Temple, Bali (Indonesia). In each group, we documented the RB frequency, prevalence and outcome, and tested the underpinning anthropogenic and demographic determinants. In line with the environmental opportunity hypothesis, we found a positive qualitative relation at the group level between time spent in tourist zones and RB frequency or prevalence. For two of the four groups, RB events were significantly more frequent when humans were more present in the environment. We also found qualitative partial support for the male-biased sex ratio hypothesis [i.e., RB was more frequent and prevalent in groups with higher ratios of (sub)adult males], whereas the group density hypothesis was not supported. This preliminary study showed that RB is a spontaneous, customary (in some groups), and enduring population-specific practice characterized by intergroup variation in Balinese macaques. As such, RB is a candidate for a new behavioral tradition in this species. 相似文献
110.
Brigitte Mangin Nicolas Pouilly Marie-Claude Boniface Nicolas B. Langlade Patrick Vincourt Felicity Vear Stéphane Muños 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2017,130(6):1099-1112