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141.
Siemer A Masip M Carreras N García-Ortega L Oñaderra M Bruix M Del Pozo AM Gavilanes JG 《Biological chemistry》2004,385(12):1165-1170
Asparagine 54 of alpha-sarcin is a conserved residue within the proteins of the ribotoxin family of microbial ribonucleases. It is located in loop 2 of the protein, which lacks repetitive secondary structure elements but exhibits a well-defined conformation. Five mutant variants at this residue have been produced and characterized. The spectroscopic characterization of these proteins indicates that the overall conformation is not changed upon mutation. Activity and denaturation assays show that Asn-54 largely contributes to protein stability, and its presence is a requirement for the highly specific inhibitory activity of these ribotoxins on ribosomes. 相似文献
142.
Under mild conditions (Lewis acid/solvent/room temperature), the reaction of unprotected glucose, deoxyribose or xylose with hydroxylalkylthymine gives selectively nucleoside analogs with a spacer arm between sugar and base moiety. Experimental conditions (Lewis acid, solvent) for this new strategy leading to nucleoside analogs synthesis are discussed. 相似文献
143.
Optimization of the preparation of aqueous suspensions of waxy maize starch nanocrystals using a response surface methodology 总被引:7,自引:0,他引:7
Response surface methodology was used to investigate the effect of five selected factors on the selective H(2)SO(4) hydrolysis of waxy maize starch granules. These predictors were temperature, acid concentration, starch concentration, hydrolysis duration, and stirring speed. The goal of this study was to optimize the preparation of aqueous suspensions of starch nanocrystals, i.e., to determine the operative conditions leading to the smallest size of insoluble hydrolyzed residue within the shortest time and with the highest yield. Therefore empirical models were elaborated for the hydrolysis yield and the size of the insoluble residues using a central composite face design involving 31 trials. They allowed us to show that it was possible to obtain starch nanocrystals after only 5 days of H(2)SO(4) hydrolysis with a yield of 15 wt % and having the same shape as those obtained from the classical procedure after 40 days of HCl treatment, with a yield of 0.5 wt %. 相似文献
144.
Sanna V Kirschvink N Gustin P Gavini E Roland I Delattre L Evrard B 《AAPS PharmSciTech》2004,5(2):17-23
The purpose of this research was to investigate the effects of processing conditions on the characteristics of solid lipid
microparticles (SLM) with a potential application as carriers for pulmonary administration. Compritol (5.0% wt/wt) SLM dispersions
were prepared by rotor-stator homogenization, at different surfactant concentrations and emulsification times. The SLM were
characterized, in terms of morphology and size, after lyophilization and sterilization by autoclaving process. In vivo assessment
was carried out in rats by intratracheal instillation of either placebo or SLM dispersion, and by bronchoalveolar lavage for
cytological analysis. Mean particle size of 4 to 5 μm was achieved using 0.3% and 0.4% (wt/wt) of emulsifier (Poloxamer 188)
and emulsification times of 2 and 5 minutes. The particles showed spherical shape and smooth surface. The morphology of microparticles,
the size, and the size distribution were not substantially modified after lyophilization and sterilization. Total cell counts
showed no significant differences between placebo and SLM 0.5% or 2.5% groups. Regarding cytology, percentage of polymorphonuclear
neutrophils and macrophages did not significantly differ between groups. These results suggest that a single intratracheal
administration of the SLMs does not induce a significant inflammatory airway response in rats and that the SLMs might be a
potential carrier for encapsulated drug via the pulmonary route. 相似文献
145.
We examined the effects of habitat fragmentation of the white-starred robin Pogonocichla stellata metapopulation in the Taita Hills archipelago, a hotspot for biodiversity which was fragmented approximately 40 years ago. Using seven microsatellite markers, we analysed the robin's genetic structure and tested for equilibrium between migration and drift (testing the probability of decreased dispersal) as well as between mutation and drift (test for recent reduction in effective population size, i.e. bottlenecks). This metapopulation was found to retain relatively high levels of genetic variability (H(E) between 0.63 and 0.71) and to be in migration-drift equilibrium, suggesting that increased isolation between fragments did not have much effect on the dispersal between them. Furthermore, this equilibrium test greatly enhanced the interpretation of parameters (e.g. F(ST)) assumed to have reached an equilibrium value. In contrast to previous findings on the related and sympatric Taita thrush Turdus helleri (which is critically endangered), there were no indications for recent bottlenecks in any of the robin subpopulations. This difference can be attributed to the higher dispersal capacity of the robin compared with the thrush (deduced from both the genetic and capture-recapture data). Our results stress the importance of sustained dispersal for species conservation. 相似文献
146.
Brooks R Bussière LF Jennions MD Hunt J 《Proceedings. Biological sciences / The Royal Society》2004,271(Z3):S64-S66
Left-handers occur at unexpectedly high frequencies at top levels of many interactive sports. This may occur either because left-handed contestants are innately superior or because they enjoy a negatively frequency-dependent strategic advantage when rare relative to right-handers. We analysed the batting records from the 2003 cricket World Cup and showed that left-handed batsmen were more successful than right-handers, and that the most successful teams had close to 50% left-handed batsmen. We demonstrate that this was because left-handed batsmen have a strategic advantage over bowlers, and that this advantage is greatest over bowlers that are unaccustomed to bowling to left-handers. This provides a clear mechanism for negative frequency-dependent success of left-handed batsmen. Our results may also support a historical role for negative frequency-dependent success in fights and other contests in the maintenance of left-handedness by natural selection. 相似文献
147.
A2B receptor activation promotes glycogen synthesis in astrocytes through modulation of gene expression 总被引:4,自引:0,他引:4
Allaman I Lengacher S Magistretti PJ Pellerin L 《American journal of physiology. Cell physiology》2003,284(3):C696-C704
Adenosinehas been proposed as a key factor regulating the metabolic balancebetween energy supply and demand in the central nervous system. Becauseastrocytes represent an important cellular element in the control ofbrain energy metabolism, we investigated whether adenosine could inducelong-term changes of glycogen levels in primary cultures of mousecortical astrocytes. We observed that adenosine increased glycogencontent, up to 300%, in a time- (maximum at 8 h) andconcentration-dependent manner with an EC50 of 9.69 µM.Pharmacological experiments using the broad-spectrum agonist5'-(N-ethylcarboxamido)adenosine (NECA) and specificagonists for the A1, A2A, and A3receptors [N6-cyclopentyladenosine (CPA),CGS-21680, and IB-MECA, respectively] suggest that the effect ofadenosine is mediated through activation of the low-affinityA2B adenosine receptor subtype. Interestingly, adenosineinduces in parallel the expression of the protein targeting to glycogen(PTG), one of the protein phosphatase-1 glycogen-targeting subunitsthat has been implicated in the control of glycogen levels in varioustissues. These results indicate that adenosine can exert long-termcontrol over glycogen levels in astrocytes and might therefore play asignificant role in physiological and/or pathological processesinvolving long-term modulation of brain energy metabolism. 相似文献
148.
Lucía Tapia Miriam Suazo Christian Hödar Verónica Cambiazo Mauricio González 《Biometals》2003,16(1):169-174
With this work, we have determined the cellular content of Cu, Fe and Zn in different cell lines, by using total reflection X-ray fluorescence spectrometry (TXRF). In addition, we examined whether cellular exposure to 100 moles l–1 of Cu-His modifies the intracellular content and distribution of these trace metals. Our results indicate that all the cell lines displayed the same pattern of relative intracellular abundance of trace metals (Cu相似文献
149.
Le Diguarher T Ortuno JC Dorey G Shanks D Guilbaud N Pierré A Fauchère JL Hickman JA Tucker GC Casara PJ 《Bioorganic & medicinal chemistry》2003,11(14):3193-3204
A rapid structure-activity study was performed by parallel liquid synthesis on N,N'-disubstitution of 3-amino azepin-2-one to afford potent and specific farnesyl transferase inhibitors with low nM enzymatic and cellular activities. The activities of the selected compounds were validated in vivo, and compounds 41a and 44a presented significant antitumour activity. 相似文献
150.
Cantu C Benlagha K Savage PB Bendelac A Teyton L 《Journal of immunology (Baltimore, Md. : 1950)》2003,170(9):4673-4682
CD1 resembles both class I and class II MHC but differs by the important aspect of presenting lipid/glycolipids, instead of peptides, to T cells. Biophysical studies of lipid/CD1 interactions have been limited, and kinetics of binding are in contradiction with functional studies. We have revisited this issue by designing new assays to examine the loading of CD1 with lipids. As expected for hydrophobic interactions, binding affinity was not high and had limited specificity. Lipid critical micelle concentration set the limitation to these studies. Once loaded onto CD1d, the recognition of glycolipids by alphabeta T cell receptor was studied by surface plasmon resonance using soluble Valpha14-Vbeta8.2 T cell receptors. The Valpha14 Jalpha18 chain could be paired with NK1.1 cell-derived Vbeta chain, or any Vbeta8 chain, to achieve high affinity recognition of alpha-galactosylceramide. Biophysical analysis indicated little effect of temperature or ionic strength on the binding interaction, in contrast to what has been seen in peptide/MHC-TCR studies. This suggests that there is less accommodation made by this TCR in recognizing alpha-galactosylceramide, and it can be assumed that the most rigid part of the Ag, the sugar moiety, is critical in the interaction. 相似文献