Search results for "HYDROLYSIS"
showing 10 items of 632 documents
Pleiotropic Role of Recombinant Silaffin-Like Cationic Polypeptide P5S3: Peptide-Induced Silicic Acid Stabilization, Silica Formation and Inhibition …
2016
Silica-mineralizing organisms such as diatoms manage several aspects of silica chemistry when polymerizing monomeric silicic acid into amorphous silica. Silicic acid is undersaturated in the diatoms’ habitats and mechanisms of enrichment and prevention of uncontrolled mineralization are not well understood. Diatom-biosilica is associated with organic compounds, including polycationic, post-translationally modified peptides termed silaffins, which induce the condensation of silicic acid under supersaturated conditions. Here, we report the pleiotropic action of the designed silaffin-like peptide P5S3, which (i) stabilizes 4–8x silicic acid (in supersaturated conditions of 8.3 mm), (ii) decele…
Protonation and rearrangement of the tricyclo[4.2.2.22,5]dodeca-3,7,9,11-tetraene scaffold
2006
The biplanemers 2a,b contain enol ether substructures, which permit facile protonations of the π electron system. The subsequent ether cleavage is characterized by rearrangements of the polycyclic scaffold of the carbenium ions or the electroneutral primary products. Apart from the expected products 3a and 5a, a series of unexpected ketones and diketones (4a′, 9b, 10b, 11b, and 12b) were obtained.
Comparison of Water Adsorption Properties of Cellulose and Cellulose Nanocrystals Studied by Near-Infrared Spectroscopy and Gravimetry
2017
The adsorption properties of water molecules on cellulose and cellulose nanocrystals (CNCs), isolated from defatted rice bran (DRB) by 55% sulfuric acid hydrolysis under sonication were investigated. The powdered samples of cellulose and CNCs were analysed by using near infrared spectroscopy (NIR) and gravimetry at 38% and 55% humidities. Small amounts of samples were dried under vacuum at 120°C and the NIR spectra of the dry samples and their spectra during the adsorption water molecules were measured by using an NIR spectrometer equipped with a transflectance accessory and a DTGS detector. The quantitative adsorption of water molecules by the samples was determined by gravimetry. Second a…
Controlled cleavage of KLH1 and KLH2 by the V8 protease from Staphylococcus aureus reassociation, electrophoretic and transmission electron microscop…
1999
The reassociation behaviour of protease V8-cleaved peptides from KLH1 and KLH2, the two hemocyanin isoforms from the giant keyhole limpet Megathura crenulata, has been studied by transmission electron microscopy of negatively stained specimens and SDS/PAGE. Reassociation of the complete mixture of protease cleavage products and of combinations of peptide fragments purified by HPLC was performed in the presence of 100 mm CaCl2 and 100 mm MgCl2 at pH 7.4, over a period of 1 to 4 weeks. The V8 protease splits KLH1 into peptide fragments containing the functional units abc, def, defg, defgh, g and h. This mixture of peptide fragments reassociated to form helical tubular polymers, with a diamete…
Two proteases from nuclei of rat testis cells. I. Isolation
1987
Abstract Two proteases, assayed with fluorogenic peptides and tentatively designated Rc and Kc, have been isolated from nuclei of rat testis cells by differential extraction with acetic acid, removal of some proteins at pH 4.5, and polyacrylamide gel electrophoresis followed by electroblotting onto nitrocellulose paper. Protease R hydrolyzes t‐Butyl‐oxycarbonyl‐Val‐Pro‐Arg‐7‐amino‐4‐methyl‐coumarin and other peptides in which arginine is joined to 7‐amino‐4‐methyl‐coumarin by amide linkage. Protease Kc has a preference for peptides terminating in lysine‐7‐amino‐4‐methylcoumarin amide. Neither of these proteases is active against Glu‐Phe‐7‐amino‐4‐methyl‐coumarin amide or Carbobenzoxy‐Arg‐7‐…
Enzyme molecular mechanism as a starting point to design new inhibitors: a theoretical study of O-GlcNAcase.
2011
O-Glycoprotein 2-acetamino-2-deoxy-β-d-glucopyranosidase (O-GlcNAcase) hydrolyzes O-linked 2-acetamido-2-deoxy-β-d-glucopyranoside (O-GlcNAc) residues from post-translationally modified serine/threonine residues of nucleocytoplasmic protein. The chemical process involves substrate-assisted catalysis, where two aspartate residues have been identified as the two key catalytic residues of O-GlcNAcase. In this report, the first step of the catalytic mechanism used by O-GlcNAcase involving substrate-assisted catalysis has been studied using a hybrid quantum mechanical/molecular mechanical (QM/MM) Molecular Dynamics (MD) calculations. The free energy profile shows that the formation of the oxazol…
On the Nature of the Enzyme–Substrate Complex and the Reaction Mechanism in Human Arginase I. A Combined Molecular Dynamics and QM/MM Study
2020
We present here a detailed theoretical analysis of L-arginine hydrolysis catalyzed by Human Arginase I (HARGI). Our study combines classical molecular dynamic simulations of different model for the...
On the Dichotomic Behavior of the Z-2,4-Dinitrophenylhydrazone of 5-Amino-3-benzoyl-1,2,4-oxadiazole with Acids in Toluene and in Dioxane/Water: Rea…
2004
The mononuclear rearrangement (MRH) of the Z-2,4-dinitrophenylhydrazone (4a) and of the Z-phenylhydrazone (4b) of 5-amino-3-benzoyl-1,2,4-oxadiazole into the relevant triazoles 5a and 5b in toluene has been quantitatively investigated in the presence of trichloroacetic acid (TCA) and of piperidine at 313.1 K. While the behavior in the presence of piperidine recalls the one previously evidenced for some Z-hydrazones of 3-benzoyl-5-phenyl-1,2,4-oxadiazole, the study of the reactivity in the presence of TCA has most interestingly evidenced a general-acid-catalyzed rearrangement for “both” 4a and 4b. Thus, 4a offers the first example of a solvent-dependent dichotomic behavior in MRH processes o…
Classification of vegetable oils according to their botanical origin using amino acid profiles established by High Performance Liquid Chromatography …
2010
Abstract A preliminary study using amino acid profiles to classify oils according to their botanical origin has been performed. Amino acid profiles were obtained from hydrolysis of proteins present in vegetable oils, and established by High Performance Liquid Chromatography (HPLC) with UV–vis detection. Proteins present in hazelnut, corn, soybean, olive, avocado, peanut and grapeseed oils were precipitated with acetone, and the residue was hydrolysed in acid medium. The amino acids obtained were derivatized with o -phthaldialdehyde and separated by HPLC. Peaks corresponding to 18 amino acids were observed using a C18 column and a gradient of acetonitrile–water in the presence of a 5 mM citr…
Pig liver esterase (PLE)-mediated resolution of N-substituted 4-benzoyloxy-3-carbomethoxypiperidines: A convenient preparation of 4-hydroxy- and 4-be…
2000
Abstract Pig liver esterase (PLE) afforded smooth chemical resolution of racemic N -substituted 4-(benzoyloxy)-3-carbomethoxypiperidines. The enzyme showed good chemo- and enantioselective properties, thus allowing discrimination between the carbomethoxy and benzoate ester groups, the latter being more easily hydrolyzed. The proposed methodology also represents a practical means for the procurement of N -substituted 4-hydroxy-3-carbomethoxypiperidines in enantiomerically pure form.