Navegando por Data de Publicação, começando com "2016-01-15"

Filtrar resultados por ano ou mês

Agora exibindo 1 - 2 de 2

Beta-glicosidases das famílias GH 1 e GH 3 : caracterização estrutural, bioquímica e mecanismos estruturais de transglicosilação
(Universidade Federal de São Carlos, 2016-01-15) Florindo, Renata Nobrega; Seleghim, Mirna Helena Regali; https://lattes.cnpq.br/5998337634888263; Polikarpov, Igor; https://lattes.cnpq.br/9669532724764871; https://lattes.cnpq.br/5594294047666889
The search for new sustainable alternative energy sources has followed the increasing concerns with common welfare and fossil fuel shortage. In this context, Bioethanol is a good option and lignocellulosic biomass is an interesting way of obtaining it. The enzymatic conversion of lignocellulosic biomass in fermentable sugars still is a costly process, which makes characterization mechanisms indispensable to make it economically viable. Being of great importance in the lignocellulosic biomass convertion, β-glucosidases catalyzed reaction is the last step in the saccharification processes. Beta glucosidase hydrolyze non-reduced β-D-glycoside terminals, releasing β-D-glucose. GH 1 and GH 3 are the families of those most studied enzymes. However, structural and functional data from this GH 3 family of enzymes are still scarce. This work aimed at the biochemical and structural characterization of β-glucosidase from Bifidobacterium adolescentis (BaBgl). This enzyme has a catalytic domain (CCD) and a fibronectin III-like domain (FnIII) whose function is still unknown. Biochemical data showed optimal conditions for enzyme activity at pH from 6.0 to 6.5, temperature at 45 ° C and synthetic substrate specificity of 4-nitrophenyl- -Dglucopyranoside (pNPG). The values of kinetic parameters, KM and Vmax, were 0.32±0.03 mM e 0.37±0.01 nmol/min, respectively. The enzyme doesn’t have transglycosylation mechanisms, indicating only hydrolytic activity. Some monosaccharides such as xylose and galactose increased the enzyme activity significantly, while glucose and arabinose inhibited it. The crystal structural model of the BaBgl revealed an N-terminal domain with fold like a TIM barrel, an intermediate sandwich α / β domain and a third C-terminal like FnIII domain. In this work we also studied the transglycosylation mechanisms of two β-glucosidases from Trichoderma harzianum (ThBgl1 and ThBgl2). Both enzymes exhibit transglycosylation reaction but the ThBgl1 showed a hydrolysis/transglycosylation ratio lower than the one for ThBgl2. Crystallographic structures shows a typical folding for GH family 1 β-glucosidases, folding in the form of a TIM barrel (α / β)8. However, ThBgl2 has a more polar active site and therefore, favorites the interaction with water molecules, promoting better the hydrolysis reaction when compared to ThBgl1.
Diferenciação e caracterização química de espécies de Phyllanthus utilizando técnicas hifenadas
(Universidade Federal de São Carlos, 2016-01-15) Sprenger, Ricardo da Fontoura; Cass, Quezia Bezerra; https://lattes.cnpq.br/9197210255594409; https://lattes.cnpq.br/0974948816384258
Several species of Phyllanthus genus are widely used in popular medicine, even though very few phytochemical reports on species such as: P. caroliniensis, P. stipulatus and P. tenellus are found in the literature. Furthermore, the official reference quality control methods, especially those related with authenticity assessment, are nonspecific for the species under analysis. Thereby, this work reports on the online chemical characterization of the ethanolic extract of six Phyllanthus species by liquid chromatography hyphenated to mass spectrometry (LC-MS) and liquid chromatography hyphenated to nuclear magnetic spectroscopy using automated solid phase extraction system, as interface (LC-SPE-NMR). The chapter 2 discusses the classification of commercial Phyllanthus samples acquired from different establishments in several Brazilian municipalities. The identification of various chemical markers from authentic samples of each species allowed the classification of commercial samples. The obtained results showed that they were misused, in spite of their labels nominating them as P. niruri, the majority of the tested samples were P. tenellus. None was classified as P. niruri. Chapter 3 discusses the use of statistical models for the chromatographic method development and also for the handling of MS data. Development of the method was carried out by experimental design furnishing chromatographic runs with short analysis time and high number of chromatographic bands. Statistical analysis using principal component analysis (PCA) allowed the unmistakable differentiation of species and pointed out to several of compounds responsible for this. Through the interpretation of the MS/MS data, using the mass analyzers QqToF and IT-MS, 22 compounds had their chemical structure elucidated, some of which have never been reported in the literature. Chapter 4 describes the results obtained by LC-SPE-NMR for the unequivocal structural elucidation of the secondary metabolites of the ethanolic extract of P. tenellus. The use of automated SPE interface facilitated the isolation of the compounds of interest, eliminating the need of using semi-preparative chromatography. The interpretation of NMR spectra enabled the identification of 9 compounds confirming the structures inferred by LC-MS.