共查询到20条相似文献,搜索用时 31 毫秒
1.
Background
Plasma lipases and lipid transfer proteins are involved in the generation and speciation of high density lipoproteins. In this study we have examined the influence of plasma lipases and lipid transfer protein activities on the transfer of free cholesterol (FC) and phospholipids (PL) from lipid emulsion to human, rat and mouse lipoproteins. The effect of the lipases was verified by incubation of labeled (3H-FC,14C-PL) triglyceride rich emulsion with human plasma (control, post-heparin and post-heparin plus lipase inhibitor), rat plasma (control and post-heparin) and by the injection of the labeled lipid emulsion into control and heparinized functionally hepatectomized rats. 相似文献2.
Abstract
Among the various lipases screened for the regioselective monoacetylation of 3-aryloxy-1,2-propanediols, porcine pancreatic lipase was found to afford a higher yield. The selectivity for the monoacetylation process was maximized by using different organic solvents and diisopropyl ether gave the highest conversion to monoacetylated product (ca. 98%). The optimized reaction afforded excellent yields of the monoacetylated product with regioselectivity at the terminal hydroxyl group in the presence of various aryl substituents in the starting material. 相似文献3.
Background
Eukaryotic aldehyde dehydrogenases (ALDHs, EC 1.2.1), which oxidize aldehydes into carboxylic acids, have been classified into more than 20 families. In mammals, Family 2 ALDHs detoxify acetaldehyde. It has been hypothesized that plant Family 2 ALDHs oxidize acetaldehyde generated via ethanolic fermentation, producing acetate for acetyl-CoA biosynthesis via acetyl-CoA synthetase (ACS), similar to the yeast pathway termed the "pyruvate dehydrogenase (PDH) bypass". Evidence for this pathway in plants has been obtained from pollen. 相似文献4.
Background
Ultrasound has been used to accelerate the rates of numerous chemical reactions, however its effects on enzymatic reactions have been less extensively studied. While known to result in the acceleration of enzyme-catalysed reactions, ultrasonication has also been shown to induce enzyme inactivation. In this study we investigated the effects of ultrasonic pretreatment on lipases in both aqueous and non-aqueous media. 相似文献5.
Background
Recently there has been increased interest in pancreatic cholesterol esterase due to correlation between enzymatic activity in vivo and absorption of dietary cholesterol. Cholesterol esterase plays a role in digestive lipid absorption in the upper intestinal tract, though its role in cholesterol absorption in particular is controversial. Serine lipases, acetylcholinesterase, butyrylcholinesterase, and cholesterol esterase belong to a large family of proteins called the α/β-hydrolase fold, and they share the same catalytic machinery as serine proteases in that they have an active site serine residue which, with a histidine and an aspartic or glutamic acid, forms a catalytic triad. The aim of this work is to study the stereoselectivity of the acyl chain binding site of the enzyme for four diastereomers of an inhibitor. 相似文献6.
Daniela Remonatto J. Vladimir de Oliveira J. Manuel Guisan Débora de Oliveira Jorge Ninow Gloria Fernandez-Lorente 《Applied biochemistry and biotechnology》2018,185(3):705-716
The performance of two new commercial low-cost lipases Eversa® Transform and Eversa® Transform 2.0 immobilized in different supports was investigated. The two lipases were adsorbed on four different hydrophobic supports. Interesting results were obtained for both lipases and for the four supports. However, the most active derivative was prepared by immobilization of Eversa® Transform 2.0 on Sepabeads C-18. Ninety-nine percent of fatty acid ethyl ester was obtained, in 3 h at 40 °C, by using hexane as solvent, a molar ratio of 4:1 (ethanol/oil), and 10 wt% of immobilized biocatalyst. The final reaction mixture contained traces of monoacylglycerols but was completely free of diacylglycerols. After four reaction cycles, the immobilized biocatalyst preserved 75% of activity. Both lipases immobilized in Sepabeads C-18 were very active with ethanol and methanol as acceptors, but they were much more stable in the presence of ethanol. 相似文献
7.
Concetta De Santi Bjørn Altermark Marcin Miroslaw Pierechod Luca Ambrosino Donatella de Pascale Nils-Peder Willassen 《BMC biochemistry》2016,17(1):1
Background
The use of metagenomics in enzyme discovery constitutes a powerful approach to access to genomes of unculturable community of microorganisms and isolate novel valuable biocatalysts for use in a wide range of biotechnological and pharmaceutical fields.Results
Here we present a novel esterase gene (lip3) identified by functional screening of three fosmid metagenomic libraries, constructed from three marine sediment samples. The sequenced positive fosmid revealed an enzyme of 281 amino acids with similarity to class 3 lipases. The 3D modeling of Lip3 was generated by homology modeling on the basis of four lipases templates [PDB ID: 3O0D, 3NGM, 3G7N, 2QUB] to unravel structural features of this novel enzyme. The catalytic triad of Lip3 was predicted to be Asp207, His267 and the catalytic nucleophile Ser150 in a conserved pentapeptide (GXSXG). The 3D model highlighted the presence of a one-helix lid able to regulate the access of the substrate to the active site when the enzyme binds a hydrophobic interface. Moreover an analysis of the external surface of Lip3 model showed that the majority of the surface regions were hydrophobic (59.6 %) compared with homologous lipases (around 35 %) used as templates. The recombinant Lip3 esterase, expressed and purified from Escherichia coli, preferentially hydrolyzed short and medium length p-nitrophenyl esters with the best substrate being p-nitrophenyl acetate. Further characterization revealed a temperature optimum of 35 °C and a pH optimum of 8.0. Lip3 exhibits a broad temperature stability range and tolerates the presence of DTT, EDTA, PMSF, β-mercaptoethanol and high concentrations of salt. The enzyme was also highly activated by NaCl.Conclusions
The biochemical characterization and homology model reveals a novel esterase originating from the marine Arctic metagenomics libraries with features of a cold-active, relatively thermostable and highly halotolerant enzyme. Taken together, these results suggest that this esterase could be a highly valuable candidate for biotechnological applications such as organic synthesis reactions and cheese ripening processes.8.
1-Ethoxyvinyl esters 3, a new type of acyl donors for enzymatic resolution of racemic alcohols, were disclosed to be superior to the contemporary major reagents, vinyl esters 1 and isopropenyl esters 2. Three features of 3 are noticeable: (1) 3 generates ethyl acetate as a single coproduct, which does not affect any enzymes, while acetaldehyde liberated from 1 deactivates some kinds of lipases. (2) The reactivity of 3 was not less than that of 1 and much higher than that of 2, and the optical purity of the products was as high as that of 1 and 2. Especially, it was generally observed that 3 showed higher reactivity than 1 for reactions using Candida rugosa lipases, one of the most commonly employed lipases, having liberal applicability to substrates but sensitive to acetaldehyde. Twelve examples of the kinetic resolution of racemic secondary alcohols (5 and 10) and one desymmetrization of meso-alcohol 7 were presented employing the acetate 3a or the octanoate 3b and four types of lipases. (3) A one-pot procedure for the preparation of 3 from the corresponding carboxylic acid and the subsequent enzymatic resolution of alcohols, which has not been reported using 1 or 2, was elucidated. The chemical and optical yields of the products by this procedure were similar to those obtained using isolated 3. 相似文献
9.
Nitin A. Randive Varun Kumar Vipin A. Nair 《Monatshefte für Chemie / Chemical Monthly》2010,43(7):1329-1332
Abstract
Water-promoted hydrothiolation and hydroamination of ethyl propiolate leading to highly regioselective and stereoselective formation of thioacrylates and β-enamino esters in excellent yields, by a simple, efficient, and environmentally friendly reaction procedure without employing any hazardous reagent or solvent is reported. 相似文献10.
Background
Electroporation is a common method to introduce foreign molecules into cells, but its molecular basis is poorly understood. Here I investigate the mechanism of pore formation by direct molecular dynamics simulations of phospholipid bilayers of a size of 256 and of more than 2000 lipids as well as simulations of simpler interface systems with applied electric fields of different strengths. 相似文献11.
Rajendra M. Srivastava Maria C. Pereira Wagner W. M. Faustino Kaline Coutinho Janaína V. dos Anjos Sebasti?o J. de Melo 《Monatshefte für Chemie / Chemical Monthly》2009,15(2):1319-1324
Abstract
A simple and easy synthesis of ten arylamidoximes from arylnitriles and hydroxylamine is described. The formation of the arylamides has been observed to a much lesser extent in the present work. A new mechanism for the formation of arylamidoximes, as well as arylamides, from arylnitriles and hydroxylamine is suggested. Quantum mechanical calculations have been carried out to support this mechanism. The enthalpy of formation in conjunction with atomic charges of the reactants and intermediates helped to understand more about the generation of the products. 相似文献12.
Mino R. Caira Emilian Georgescu Florentina Georgescu Florin Albota Florea Dumitrascu 《Monatshefte für Chemie / Chemical Monthly》2011,62(2):743-748
Abstract
Structural elucidation of the dihydro derivatives obtained as by-products in the classic salt method synthesis of pyrrolo[2,1-a]phthalazines and acetylenic dipolarophiles was achieved by X-ray diffraction analysis of a representative compound. In addition, new pyrrolo[2,1-a]phthalazines were obtained by a one-pot three-component reaction that avoids the formation of the dihydro derivative intermediates. 相似文献13.
The kinetic mechanism for the formation and decay of HCO(0,0,0) following flashlamp excitation (10 μs pulse width) into the 1A″ → 1A′ absorption transition of gas phase acetaldehyde (0.2 Torr) was examined by time-resolved intracavity laser detection (TRMD) and by phosphorescence lifetime measurements. The HCO radical was found to appear primarily in the vibrationless level reaching a maximum concentration about 250 μs after the excitation of acetaldehyde. The formation rate of HCO(0,0,0) was observed to be insensitive to an order of magnitude change in the number of collisions of excited-state acetaldehyde with either argon, cyclohexane, or the cell wall. Contrastingly, the decay rate of HCO exhibited a strong dependence on the collisional environment. The rate constants for HCO(0,0,0) decay by collisions with acetaldehyde, argon, and cyclohexane and by reaction with O2 were measured by TRILD. The rate constant for O2, quenching of 3A″ phosphorescence was also obtained.The potential for HCO(0,0,0) being either a primary or secondary dissociation product is considered in the formulation of a kinetic mechanism describing both the formation and decay behavior observed. Evidence is presented in support of a mechanism in which (1) HCO(0,0,0) is formed by the thermal reaction between acetyl radicals. CH3CO, and ground-state acetaldehyde after excited-state acetaldehyde undergoes primary dissociation to CH3CO, and (2) HCO(0,0,0) decays principally by collisionally-induced dissociation at the cell wall. 相似文献
14.
M.J.S. Farias G.A. Camara A.A. Tanaka T. Iwasita 《Journal of Electroanalytical Chemistry》2007,600(2):236-242
Parallel pathways forming CO2 and acetic acid occur during the electrooxidation of acetaldehyde at Pt in acid medium. The yields of products depend on potential and acetaldehyde concentration. In the whole range of concentrations investigated (2.5 × 10−3 – 0.5 M) and at potentials below 0.6 V, CO2 is the only product of acetaldehyde oxidation. Acetic acid is detected at potentials higher than 0.7 V. According to the analysis of products using FTIR spectroscopy, a maximum yield of CO2 production is obtained for an acetaldehyde concentration of 0.01 M at 0.6 V. The pathway forming CO2 is strongly inhibited for 0.5 M of acetaldehyde. It is suggested that, at high concentrations, a competition with water for active sites occurs, which inhibits the oxidation of adsorbed species, which probably follow a Langmuir–Hinshelwood mechanism. 相似文献
15.
Background
A third DNA strand can bind into the major groove of a homopurine duplex DNA to form a DNA triple helix. Sequence specific triplex formation can be applied for gene targeting, gene silencing and mutagenesis. 相似文献16.
Background
The plasminogen activator inhibitor-1 (PAI-1) spontaneously converts from an inhibitory into a latent form. Specificity of PAI-1 is mainly determined by its reactive site (Arg346-Met347), which interacts with serine residue of tissue-type plasminogen activator (tPA) with concomitant formation of SDS-stable complex. Other sites may also play roles in determining the specificity of PAI-1 toward serine proteases. 相似文献17.
Reduction of aldehydes and hydrogen cyanide yields in mainstream cigarette smoke using an amine functionalised ion exchange resin 总被引:1,自引:0,他引:1
Background
Cigarette smoking is a well recognized cause of diseases such as lung cancer, chronic obstructive pulmonary disease and cardiovascular disease. Of the more than 5000 identified species in cigarette smoke, at least 150 have toxicological activity. For example, formaldehyde and acetaldehyde have been assigned as Group 1 and Group 2B carcinogens by IARC, and hydrogen cyanide has been identified as a respiratory and cardiovascular toxicant. Active carbon has been shown to be an effective material for the physical adsorption of many of the smoke volatile species. However, physical adsorption of acetaldehyde, formaldehyde and also hydrogen cyanide from smoke is less effective using carbon. Alternative methods for the removal of these species from cigarette smoke are therefore of interest. A macroporous, polystyrene based ion-exchange resin (Diaion®CR20) with surface amine group functionality has been investigated for its ability to react with aldehydes and HCN in an aerosol stream, and thus selectively reduce the yields of these compounds (in particular formaldehyde) in mainstream cigarette smoke.Results
Resin surface chemistry was characterized using vapour sorption, XPS, TOF-SIMS and 15N NMR. Diaion®CR20 was found to have structural characteristics indicating weak physisorption properties, but sufficient surface functionalities to selectively remove aldehydes and HCN from cigarette smoke. Using 60 mg of Diaion®CR20 in a cigarette cavity filter gave reductions in smoke formaldehyde greater than 50% (estimated to be equivalent to >80% of the formaldehyde present in the smoke vapour phase) independent of a range of flow rates. Substantial removal of HCN (>80%) and acetaldehyde (>60%) was also observed. The performance of Diaion®CR20 was found to be consistent over a test period of 6 months. The overall adsorption for the majority of smoke compounds measured appeared to follow a pseudo-first order approximation to second order kinetics.Conclusions
This study has shown that Diaion®CR20 is a highly selective and efficient adsorbent for formaldehyde, acetaldehyde and HCN in cigarette smoke. The reductions for these compounds were greater than those achieved using an active carbon. The results also demonstrate that chemisorption can be an effective mechanism for the removal of certain vapour phase toxicants from cigarette smoke.18.
Background
Water-soluble quinoprotein glucose dehydrogenase (PQQGDH-B) from Acinetobacter calcoaceticus has a great potential for application as a glucose sensor constituent. Because this enzyme shows no activity in its monomeric form, correct quaternary structure is essential for the formation of active enzyme. We have previously reported on the increasing of the stability of PQQGDH-B by preventing the subunit dissociation. Previous studies were based on decreasing the entropy of quaternary structure dissociation but not on increasing the interaction between the two subunits. We therefore attempted to introduce a hydrophobic interaction in the dimeric interface to increase the stability of PQQGDH-B. 相似文献19.
Ariela Veloso de Paula Gisele Fátima Morais Nunes Josiane de Lourdes Silva Heizir Ferreira de Castro Júlio César dos Santos 《Applied biochemistry and biotechnology》2010,160(4):1146-1156
Seven food grade commercially available lipases were immobilized by covalent binding on polysiloxane–polyvinyl alcohol (POS-PVA)
hybrid composite and screened to mediate reactions of industrial interest. The synthesis of butyl butyrate and the interesterification
of tripalmitin with triolein were chosen as model reactions. The highest esterification activity (240.63 μM/g min) was achieved
by Candida rugosa lipase, while the highest interesterification yield (31%, in 72 h) was achieved by lipase from Rhizopus oryzae, with the production of about 15 mM of the triglycerides C50 and C52. This lipase also showed a good performance in butyl butyrate synthesis, with an esterification activity of 171.14 μM/g min.
The results demonstrated the feasibility of using lipases from C. rugosa for esterification and R. oryzae lipase for both esterification and interesterification reactions. 相似文献
20.
Miguel A Treviño Mar Rodríguez-Rodríguez Isabel Correas Miguel Marcilla Juan P Albar Manuel Rico M Ángeles Jiménez Marta Bruix 《BMC biochemistry》2010,11(1):7