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Background
Experimentally determined protein structures may contain errors and require validation. Conformational criteria based on the Ramachandran plot are mainly used to distinguish bet ween distorted and adequately refined models. While the readily available criteria are sufficient to detect totally wrong structures, establishing the more subtle differences between plausible structures remains more challenging. 相似文献23.
24.
The taste of polycose in hamsters 总被引:2,自引:2,他引:0
Hamsters show a preference for Polycose, a mixture of starch-derived
glucose polymers, that is as strong as their preference for sucrose.
However, in the hamster, taste aversions to Polycose may be less easily
acquired than taste aversions to sucrose and the qualitative aspects of
Polycose are unknown in this species. In order to examine the taste of
Polycose in the hamster, we utilized a taste-aversion protocol with two
conditioning trials. Animals were trained to avoid one of three different
conditioning stimuli: 50 mM sucrose, 100 mM Polycose and a mixture of 50 mM
sucrose with 100 mM Polycose. Control animals were conditioned with
deionized water. After the second conditioning trial, generalization
testing began for the three conditioning stimuli plus 3 mM citric acid, 300
mM KCI and 30 mM NaCl. The results showed that aversions to Polycose,
sucrose or the Polycose/sucrose mixture cross- generalized, demonstrating
that Polycose and sucrose share a common taste percept in the hamster. None
of the aversions generalized to NaCl, citric acid or KCI. In addition,
comparisons among the patterns of taste generalizations indicated that the
tastes of Polycose and sucrose also had distinct qualitative components.
Finally, although the taste of 100 mM Polycose was more salient than the
taste of 50 mM sucrose, the taste of sucrose could still be detected in a
mixture with Polycose.
相似文献
25.
Purification of galectin-3 from ovine placenta: developmentally regulated expression and immunological relevance 总被引:1,自引:1,他引:1
Iglesias MM; Rabinovich GA; Ambrosio AL; Castagna LF; Sotomayor CE; Wolfenstein-Todel C 《Glycobiology》1998,8(1):59-65
Galectins, beta-galactoside-binding lectins, are extensively distributed in
the animal kingdom and share some basic molecular properties. Galectin-3, a
member of this family, is generally associated with differentiation,
morphogenesis, and metastasis. In this study, galectin-3 was isolated from
ovine placental cotyledons round the middle of the gestation period by
lactose extraction followed by affinity chromatography on lactosyl-agarose,
and separated from galectin-1 by size exclusion chromatography on a
Superose 12 column. Under native conditions this lectin behaved as a
monomer with an apparent molecular weight of approximately 29,000 and an
isoelectric point of 9.0. The partial amino acid sequence of the peptides
obtained by tryptic digestion of this protein followed by HPLC separation
showed striking homology with other members of the galectin-3 subfamily.
Furthermore, ovine placental galectin-3 exhibited specific mitogenic
activity toward rat spleen mononuclear cells. Besides, this protein
strongly reacted with a rabbit antiserum raised against a chicken galectin.
Results obtained by Western blot analysis showed that its expression was
greatly decreased in term placenta with respect to the middle of the
gestation period, suggesting a regulated expression throughout development.
相似文献
26.
黄檗丛枝菌根真菌鉴定 总被引:1,自引:0,他引:1
目的:利用形态学特征与Nested-PCR技术鉴定黄檗丛枝菌根真菌。方法:采用酸性品红染色法挑选黄檗丛枝菌根。同时,利用湿筛法获得AM真菌孢子,进行形态学鉴定。运用Nested-PCR技术,对黄檗粗提DNA进行特异性扩增,采用blastn进行序列相似性比较。并构建系统进化树,确定侵染黄檗根系的AM真菌。结果:编号为HDAM-1的AM真菌孢子,形态特征与G.intraradices的特征描述一致。Nested-PCR检测到约455bp的目的片段,其序列与G.intraradices(DQ469118)相似性最高,达97.8%,有11个碱基的差异。系统进化树显示该序列在基于25S rDNA的进化树中与G.intraradices(DQ469118.1)处于同一分支,确定G.intraradices侵染黄檗根系。结论:将形态学特征与Nested-PCR技术相结合鉴定AM真菌,不仅简易、经济,而且能够提高研究结果的可靠性。 相似文献
27.
Marjolijn CE Bragt Jogchum Plat Marco Mensink Patrick Schrauwen Ronald P Mensink 《BMC endocrine disorders》2009,9(1):1-9
Background
The aim of this study is to perform a cost-effectiveness comparison between palpation-guided thyroid fine-needle aspiration biopsies (P-FNA) and ultrasound-guided thyroid FNA biopsies (USG-FNA).Methods
Each nodule was considered as a case. Diagnostic steps were history and physical examination, TSH measurement, Tc99m thyroid scintigraphy for nodules with a low TSH level, initial P-FNA versus initial USG-FNA, repeat USG-FNA for nodules with initial inadequate P-FNA or USG-FNA, hemithyroidectomy for inadequate repeat USG-FNA. American Thyroid Association thyroid nodule management guidelines were simulated in estimating the cost of P-FNA strategy. American Association of Clinical Endocrinologists guidelines were simulated for USG-FNA strategy. Total costs were estimated by adding the cost of each diagnostic step to reach a diagnosis for 100 nodules. Strategy cost was found by dividing the total cost to 100. Incremental cost-effectiveness ratio (ICER) was calculated by dividing the difference between strategy cost of USG-FNA and P-FNA to the difference between accuracy of USG-FNA and P-FNA. A positive ICER indicates more and a negative ICER indicates less expense to achieve one more additional accurate diagnosis of thyroid cancer for USG-FNA.Results
Seventy-eight P-FNAs and 190 USG-FNAs were performed between April 2003 and May 2008. There were no differences in age, gender, thyroid function, frequency of multinodular goiter, nodule location and diameter (median nodule diameter: 18.4 mm in P-FNA and 17.0 mm in USG-FNA) between groups. Cytology results in P-FNA versus USG-FNA groups were as follows: benign 49% versus 62% (p = 0.04), inadequate 42% versus 29% (p = 0.03), malignant 3% (p = 1.00) and indeterminate 6% (p = 0.78) for both. Eleven nodules from P-FNA and 18 from USG-FNA group underwent surgery. The accuracy of P-FNA was 0.64 and USG-FNA 0.72. Unit cost of P-FNA was 148 Euros and USG-FNA 226 Euros. The cost of P-FNA strategy was 534 Euros and USG-FNA strategy 523 Euros. Strategy cost includes the expense of repeat USG-FNA for initial inadequate FNAs and surgery for repeat inadequate USG-FNAs. ICER was -138 Euros.Conclusion
Universal application of USG-FNA for all thyroid nodules is cost-effective and saves 138 Euros per additional accurate diagnosis of benign versus malignant thyroid nodular disease.Trial registration
ClinicalTrials.gov, NCT00571090 相似文献28.
29.
Bayesian adaptive sequence alignment algorithms 总被引:3,自引:1,他引:2
The selection of a scoring matrix and gap penalty parameters continues to
be an important problem in sequence alignment. We describe here an
algorithm, the 'Bayes block aligner, which bypasses this requirement.
Instead of requiring a fixed set of parameter settings, this algorithm
returns the Bayesian posterior probability for the number of gaps and for
the scoring matrices in any series of interest. Furthermore, instead of
returning the single best alignment for the chosen parameter settings, this
algorithm returns the posterior distribution of all alignments considering
the full range of gapping and scoring matrices selected, weighing each in
proportion to its probability based on the data. We compared the Bayes
aligner with the popular Smith-Waterman algorithm with parameter settings
from the literature which had been optimized for the identification of
structural neighbors, and found that the Bayes aligner correctly identified
more structural neighbors. In a detailed examination of the alignment of a
pair of kinase and a pair of GTPase sequences, we illustrate the
algorithm's potential to identify subsequences that are conserved to
different degrees. In addition, this example shows that the Bayes aligner
returns an alignment-free assessment of the distance between a pair of
sequences.
相似文献
30.
The bacterial enzyme histidine decarboxylase (Hdc) catalyses the conversion of histidine into histamine. This amine is essential for the biosynthesis of iron chelators (siderophores) and is an important cause of food poisoning after consumption of fish contaminated with histamine-producing bacteria. In this work we compared different methods for detecting histamine secreted by different bacterial strains. The presence of histamine in the culture supernatant of Vibrio anguillarum, which produces Hdc and secretes the histamine-containing siderophore anguibactin, was detected by thin-layer chromatography. Similar results were obtained using the culture supernatant of the Acinetobacter baumannii 19606 prototype strain that secretes the histamine-containing siderophore acinetobactin. Conversely, histamine was not detected in the culture supernatant of an isogenic V. anguillarum Hdc mutant and the A. baumannii 8399 strain that secretes a catechol siderophore different from anguibactin and acinetobactin. These results were confirmed by capillary gas chromatography/mass spectrometry. However, all these strains tested positive for histamine secretion when cultured on differential plating media containing histidine and a pH indicator, which were specifically designed for the detection of histamine-producing bacteria. The pH increase of the medium surrounding the bacterial colonies was however drastically reduced when the histidine-containing medium was supplemented with peptone, beef extract, and glucose. The histidine-containing culture supernatants of the A. baumannii and V. anguillarum strains showed an increase of about two units of pH, turned purple upon the addition of cresol red, and contained high amounts of ammonia. Escherichia coli strains, which are Hdc negative and do not use histidine as a carbon, nitrogen, and energy source, gave negative results with the differential solid medium and produced only moderate amounts of ammonia when cultured in the presence of excess histidine. This study demonstrates that, although more laborious and requiring some expensive equipment, thin-layer and gas chromatography/mass spectrometry are more accurate than differential media for detecting bacterial histamine secretion. The results obtained with these analytical methods are not affected by byproducts such as ammonia, which are generated during the degradation of histidine and produce false positive results with the differential plating media. 相似文献