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991.
Purification and characterization of GlcNAc-6-P 2-epimerase from Escherichia coli K92 总被引:1,自引:0,他引:1
Ferrero MA Martínez-Blanco H Lopez-Velasco FF Ezquerro-Sáenz C Navasa N Lozano S Rodríguez-Aparicio LB 《Acta biochimica Polonica》2007,54(2):387-399
N-Acetylmannosamine (ManNAc) is the first committed intermediate in sialic acid metabolism. Thus, the mechanisms that control intracellular ManNAc levels are important regulators of sialic acid production. In prokaryotic organisms, UDP-N-acetylglucosamine (GlcNAc) 2-epimerase and GlcNAc-6-P 2-epimerase are two enzymes capable of generating ManNAc from UDP-GlcNAc and GlcNAc-6-P, respectively. We have purified for the first time native GlcNAc-6-P 2-epimerase from bacterial source to apparent homogeneity (1 200 fold) using Butyl-agarose, DEAE-FPLC and Mannose-6-P-agarose chromatography. By SDS/PAGE the pure enzyme showed a molecular mass of 38.4 +/- 0.2 kDa. The maximum activity was achieved at pH 7.8 and 37 degrees C. Under these conditions, the K(m) calculated for GlcNAc-6-P was 1.5 mM. The 2-epimerase activity was activated by Na(+) and inhibited by mannose-6-P but not mannose-1-P. Genetic analysis revealed high homology with bacterial isomerases. GlcNAc-6-P 2-epimerase from E. coli K92 is a ManNAc-inducible protein and is detected from the early logarithmic phase of growth. Our results indicate that, unlike UDP-GlcNAc 2-epimerase, which promotes the biosynthesis of sialic acid, GlcNAc-6-P 2-epimerase plays a catabolic role. When E. coli grows using ManNAc as a carbon source, this enzyme converts the intracellular ManNAc-6-P generated into GlcNAc-6-P, diverting the metabolic flux of ManNAc to GlcNAc. 相似文献
992.
Leandro C. S. Assis 《Cladistics : the international journal of the Willi Hennig Society》2015,31(3):315-320
The present paper is mainly concerned with homology assessment through phylogenetic analyses. It raises a fundamental question: What are the epistemological differences between modern parsimony and model‐based analyses in relation to homology assessment and phylogenetic inference? Although these methods usually achieve concordant topological results, they may generate discordant inferences of character evolution from the same datasets. This indicates that method selection has serious implications for evolutionary scenarios and classificatory arrangements. Notwithstanding that parsimony and model‐based approaches use the Hennigian concepts of monophyly and synapomorphy, they employ different epistemological ways of dealing with the monophyly/synapomorphy relationship. Independently of their differences, these analyses should take into account all relevant evidence in support of the phylogenetic inferences. A focus on morphological homologues means that they must be included in data matrices, evaluated as part of the phylogenetic analysis, and cannot be ignored in calculation of the tree(s) length (parsimony), maximum‐likelihood (maximum‐likelihood), and posterior probabilities (Bayes). 相似文献
993.
Monica Cristina Souza Louisy Sanches dos Santos Leonardo Paiva Sousa Yuri Vieira Faria Juliana Nunes Ramos Priscila Soares Sabbadini Cíntia Silva da Santos Prescilla Emy Nagao Verônica Viana Vieira Débora Leandro Rama Gomes Raphael Hirata Júnior Ana Luiza Mattos-Guaraldi 《Antonie van Leeuwenhoek》2015,107(6):1387-1399
994.
Maldonado LM Hernández VE Rivero EM Barba de la Rosa AP Flores JL Acevedo LG De León Rodríguez A 《Biomolecular engineering》2007,24(2):217-222
A human interferon beta (hINF-beta) synthetic gene was optimized and expressed in Escherichia coli BL21-SI using a vector with the T7 promoter. To determine the best culture conditions such as culture medium, temperature, cell density and inducer concentration, we used the response surface methodology and a Box-Behnken design to get the highest hINF-beta production. The maximum hINF-beta production of 61 mg l(-1) was attained using minimum medium and the following predicted optimal conditions: temperature of 32.5 degrees C, cell density of 0.64, and inducer concentration of 0.30 M NaCl. This is the first report showing the successful performance of the BL21-SI system in a minimum medium. The response surface methodology is effective for the optimization of recombinant protein production using synthetic genes. 相似文献
995.
Cervia D Garcia-Gil M Simonetti E Di Giuseppe G Guella G Bagnoli P Dini F 《Apoptosis : an international journal on programmed cell death》2007,12(8):1349-1363
The metabolite euplotin C (EC), isolated from the marine ciliate Euplotes crassus, is a powerful cytotoxic and pro-apoptotic agent in tumour cell lines. For instance, EC induces the rapid depletion of ryanodine
Ca2+ stores, the release of cytochrome c from the mitochondria, and the activation of caspase-3, leading to apoptosis. The purpose of this study was to gain further
insight into the mechanisms of EC-induced apoptosis in rat pheochromocytoma PC12 cells. We found that EC increases Bax/Bcl-2
ratio and that Bax is responsible of the EC-induced dissipation of the mitochondrial membrane potential (Δψm). In addition, EC induces the generation of reactive oxygene species (ROS) without involvement of p53. The inhibition of
ROS generation prevents, at least in part, the pro-apoptotic effects of EC as well as the effects of EC on Bax, Δψm and intracellular free Ca2+, indicating a cross-talk between different pathways. However, definition of the effector cascade turns out to be more complex
than expected and caspase-independent mechanisms, acting in parallel with caspases, should also be considered. Among them,
EC increases the expression/activity of calpains downstream of ROS generation, although calpains seem to exert protective
effects.
D. Cervia and M. Garcia-Gil equally contributed to the work. 相似文献
996.
997.
Giuseppe Pastura Thomas Doering Emerson Leandro Gasparetto Paulo Mattos Alexandra Prüfer Araújo 《Attention deficit and hyperactivity disorders》2016,8(2):65-71
Abnormalities in the white matter microstructure of the attentional system have been implicated in the aetiology of attention deficit hyperactivity disorder (ADHD). Diffusion tensor imaging (DTI) is a promising magnetic resonance imaging (MRI) technology that has increasingly been used in studies of white matter microstructure in the brain. The main objective of this work was to perform an exploratory analysis of white matter tracts in a sample of children with ADHD versus typically developing children (TDC). For this purpose, 13 drug-naive children with ADHD of both genders underwent MRI using DTI acquisition methodology and tract-based spatial statistics. The results were compared to those of a sample of 14 age- and gender-matched TDC. Lower fractional anisotropy was observed in the splenium of the corpus callosum, right superior longitudinal fasciculus, bilateral retrolenticular part of the internal capsule, bilateral inferior fronto-occipital fasciculus, left external capsule and posterior thalamic radiation (including right optic radiation). We conclude that white matter tracts in attentional and motor control systems exhibited signs of abnormal microstructure in this sample of drug-naive children with ADHD. 相似文献
998.
Agrobacterium-mediated transformation of sweet orange and regeneration of transgenic plants 总被引:1,自引:6,他引:1
Leandro Peña Magdalena Cervera José Juárez Antonio Navarro José A. Pina Nuria Durán-Vila Luis Navarro 《Plant cell reports》1995,14(10):616-619
Summary Transgenic sweet orange (Citrus sinensis L. Osbeck) plants have been obtained by Agrobacterium tumefaciens-mediated gene transfer. An hypervirulent A. tumefaciens strain harboring a binary vector that contains the chimeric neomycin phosphotransferase II (NPT II) and ß-glucuronidase (GUS) genes was cocultivated with stem segments from in vivo grown seedlings. Shoots regenerated under kanamycin selection were harvested from the stem segments within 12 weeks. Shoot basal portions were assayed for GUS activity and the remaining portions were shoot tip grafted in vitro for production of plants. Integration of the GUS gene was confirmed by Southern analysis. This transformation procedure showed the highest transgenic plant production efficiency reported for Citrus.Abbreviations BA
benzyladenine
- CaMV
cauliflowermosaic virus
- GUS
ß-glucuronidase
- LB
Luria Broth
- MS
Murashige and Skoog
- NAA
naphthalenacetic acid
- NOS
nopaline synthase
- NPT II
neomycin phosphotransferase II
- PEG
polyethylene glycol
- RM
rooting medium
- SRM
shoot regeneration medium 相似文献
999.
G Ferretti A M Offidani O Simonetti M Valentino G Curatola G Bossi 《Biochemical medicine and metabolic biology》1989,41(2):132-138
Using fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene and its cationic derivative, 1-(4-trimethylaminophenyl)-6-phenyl-1,3,5-hexatriene, we evaluated membrane fluidity in living polymorphonuclear leukocytes and in erythrocytes of psoriatic patients. Our results have shown that erythrocyte membranes of psoriatic patients exhibit a decrease of fluidity. These changes were not associated with any relevant modifications of the cholesterol to phospholipid molar ratio. Moreover, we observed a decrease in polymorphonuclear leukocytes membrane fluidity associated with changes in chemotactic migration. Our results indicate changes of membrane fluidity involving membranes different from the epidermal cells and suggest the hypothesis of a defective membrane-cytoskeleton interaction in psoriasis. 相似文献
1000.
Juliana Mendes Campolina Carolina São Leandro Sigrist Jane Maria Faulstich de Paiva Andréa Oliveira Nunes Virgínia Aparecida da Silva Moris 《The International Journal of Life Cycle Assessment》2017,22(12):1957-1968