Search results for "Hydrolases"
showing 10 items of 393 documents
Prognostic Impact of let-7e MicroRNA and Its Target Genes in Localized High-Risk Intestinal GIST: A Spanish Group for Research on Sarcoma (GEIS) Study
2020
MicroRNAs (miRNAs) are small non-coding RNAs that negatively regulate gene expression at the post-transcriptional level, and they have been described as being associated with tumor prognosis. Here, miRNA profiling was planned to explore new molecular prognostic biomarkers in localized intestinal high-risk GIST. Paraffin tumor blocks of 14 and 86 patients were used in the discovery and expansion sets, respectively. GeneChip miRNA v3.0 was employed to identify the miRNAs differentially expressed between relapsed and non-relapsed patient samples, which were validated in the expansion set, by qRT-PCR. RT2 Profiler PCR Array was used for the screening of let-7e targets. Expression levels were co…
Stereoselective Synthesis of the Glycosidase Inhibitor Australine through a One-Pot, Double-Cyclization Strategy
2006
[reaction: see text] A stereocontrolled, convergent synthesis of the alkaloid australine, a glycosidase inhibitor of the pyrrolizidine class, is described. The chiral starting materials were ketone 3, derived from L-erythrulose, and alpha-alkoxy aldehyde 4, prepared from L-malic acid. A key step of the synthesis was the highly stereoselective aldol reaction between 4 and a Z boron enolate derived from 3. Another key step was the one-pot construction of the bicyclic pyrrolizidine system by means of a three-step sequence of SN2 displacements induced by benzylamine on a trimesylate precursor.
Improving lipase activity in solvent-free media by interfacial activation-based molecular bioimprinting
1997
Abstract Nine lipases of mammalian, fungal and bacterial origin and two different model reactions, direct esterification and transesterification (alcoholysis), have been used to probe the potential in solvent-free media of the recently reported strategy of interfacial activation-based molecular (bio)imprinting (IAMI) [Mingarro et al., Proc. Natl. Acad. Sci. USA , 92 (1995) 3308]. The results demonstrate that the imprinting treatment permits nonaqueous rate accelerations which are lipase-dependent and span in some cases up to higher than two orders of magnitude. For several lipases, the method allows conversion yields after short reaction times (in either of the model reactions assayed) whic…
Epoxide Hydrolases: Structure, Function, Mechanism, and Assay
2005
Epoxide hydrolases are a class of enzymes important in the detoxification of genotoxic compounds, as well as in the control of physiological signaling molecules. This chapter gives an overview on the function, structure, and enzymatic mechanism of structurally characterized epoxide hydrolases and describes selected assays for the quantification of epoxide hydrolase activity.
Isolation and characterization of a chlorogenic acid esterase from Aspergillus niger.
1980
Abstract The isolation and characterization of a specific chlorogenic acid esterase is described. The enzyme activity is measured by determination of the hydrolysis product caffeic acid. The enzyme had been concentrated by means of ultrafiltration and column-chromatography. The pH- and temperature optimum were 6.5 and 45 °C respectively. Divalent cations were not required for the enzyme activity. As other esterases, this enzyme is inhibited by di-isopropyl-phosphorofluoridate. The Km-value is 0.70 mᴍ chlorogenic acid, the molecular weight 240000. The described enzyme is specific for chlorogenic acid. On the other hand a typical unspecific esterase like the pig liver esterases does not split…
Detoxication Strategy of Epoxide Hydrolase—The Basis for a Novel Threshold for Definable Genotoxic Carcinogens
2004
From our recent work on the three-dimensional structure of epoxide hydrolases we theoretically deduced the likelihood of a two-step catalytic mechanism that we and others have subsequently experimentally confirmed. Analysis of the rate of the two steps by us and by others show that the first step—responsible for removal of the reactive epoxide from the system—works extraordinarily fast (typically three orders of magnitude faster than the second step), sucking up the epoxide like a sponge. Regeneration of the free enzyme (the second step of the catalytic mechanism) is slow. This becomes a toxicological problem only at doses of the epoxide that titrate the enzyme out. Our genotoxicity work s…
Significance of various enzymes in the control of reactive metabolites
1987
Most chemical carcinogens are relatively inert and need metabolic activation to the ultimately carcinogenic species. The concentration of such species is controlled by several different enzymes. Especially well studied is the important group of enzymes responsible for the control of reactive epoxides. Many natural, as well as man-made foreign compounds, including pharmaceuticals, possess olefinic or aromatic double bonds. Such compounds can be transformed to epoxides by microsomal monooxygenases present in many mammalian organs. By virtue of their electrophilic reactivity, such epoxides may spontaneously react with nucleophilic centres in the cell and thus covalently bind to DNA, RNA and pr…
Rapid classification of enzymes in cleaning products by hydrolysis, mass spectrometry and linear discriminant analysis
2008
A method for the rapid classification of proteases, lipases, amylases and cellulases used as enhancers in cleaning products, based on precipitation with acetone, hydrolysis with HCl, dilution of the hydrolysates with ethanol, and direct infusion into the electrospray ion source of an ion-trap mass spectrometer, has been developed. The abundances of the ([M+H]+ ions of the amino acids, from the hydrolysates of both the enzyme industrial concentrates and the detergent bases spiked with them, were used to construct linear discriminant analysis models, capable of distinguishing between the enzyme classes. For this purpose, the variables were normalized as follows: (A) the ion abundance of each …
Purification of rat liver epoxide hydratase to apparent homogeneity.
1975
Epoxide hydratase (EC 4.2.1.63) is a microsomal enzyme which catalyses the conversion of epoxides to trans-dihydrodiols. Epoxides, produced by the action of microsomal monooxygenases (EC 1.14.1.1) from aromatic and olefinic compounds, are thought to be responsible for many of the harinful effects of polycyclic hydrocarbons and related compounds. Thus epoxide hydratase, together with glutathione 9transferases, (EC 2.5.1.18) may play an important role in the removal of carcinogenic and cytotoxic metabolites (for reviews see [l-3]). It has been reported [4,5] that dihydrodiols formed from some polycyclic hydrocarbons (benz(a)anthracene and benzo(a)pyrene) are reactivated by the microsomal mono…
The Catalytic Mechanism of Carboxylesterases: A Computational Study
2014
The catalytic mechanism of carboxylesterases (CEs, EC 3.1.1.1) is explored by computational means. CEs hydrolyze ester, amide, and carbamate bonds found in xenobiotics and endobiotics. They can also perform transesterification, a reaction important, for instance, in cholesterol homeostasis. The catalytic mechanisms with three different substrates (ester, thioester, and amide) have been established at the M06-2X/6-311++G**//B3LYP/6-31G* level of theory. It was found that the reactions proceed through a mechanism involving four steps instead of two as is generally proposed: (i) nucleophilic attack of serine to the substrate, forming the first tetrahedral intermediate, (ii) formation of the ac…