scholarly journals Kinetics of Torpedo californica acetylcholinesterase inhibition by bisnorcymserine and crystal structure of the complex with its leaving group

2012 ◽  
Vol 444 (2) ◽  
pp. 269-277 ◽  
Author(s):  
Cecilia Bartolucci ◽  
Jure Stojan ◽  
Qian-sheng Yu ◽  
Nigel H. Greig ◽  
Doriano Lamba
Keyword(s):  
Crystal Structure ◽  
Kinetic Studies ◽  
Catalytic Triad ◽  
Acetylcholinesterase Inhibition ◽  
Inhibition Mechanism ◽  
Torpedo Californica ◽  
Irreversible Inhibitors ◽  
Leaving Group ◽  
Ad Alzheimer’S Disease ◽  
Kinetics Of

Natural and synthetic carbamates act as pseudo-irreversible inhibitors of AChE (acetylcholinesterase) as well as BChE (butyrylcholinesterase), two enzymes involved in neuronal function as well as in the development and progression of AD (Alzheimer's disease). The AChE mode of action is characterized by a rapid carbamoylation of the active-site Ser200 with release of a leaving group followed by a slow regeneration of enzyme action due to subsequent decarbamoylation. The experimental AD therapeutic bisnorcymserine, a synthetic carbamate, shows an interesting activity and selectivity for BChE, and its clinical development is currently being pursued. We undertook detailed kinetic studies on the activity of the carbamate bisnorcymserine with Tc (Torpedo californica) AChE and, on the basis of the results, crystallized the complex between TcAChE and bisnorcymserine. The X-ray crystal structure showed only the leaving group, bisnoreseroline, trapped at the bottom of the aromatic enzyme gorge. Specifically, bisnoreseroline interacts in a non-covalent way with Ser200 and His440, disrupting the existing interactions within the catalytic triad, and it stacks with Trp84 at the bottom of the gorge, giving rise to an unprecedented hydrogen-bonding contact. These interactions point to a dominant reversible inhibition mechanism attributable to the leaving group, bisnoreseroline, as revealed by kinetic analysis.

scholarly journals Kinetic studies and predictions on the hydrolysis and aminolysis of esters of 2-S-phosphorylacetates

2010 ◽  
Vol 6 ◽  
pp. 732-741 ◽  
Author(s):  
Milena Trmčić ◽  
David R W Hodgson
Keyword(s):  
Reaction Times ◽  
Kinetic Studies ◽  
Cross Linking ◽  
Significant Difference ◽  
Leaving Group ◽  
Leaving Groups ◽  
Phosphoryl Groups ◽  
Kinetics Of ◽  
Hydrolysis Of ◽  
Acid Esters

Background: Heterobifunctional cross-linking agents are useful in both protein science and organic synthesis. Aminolysis of reactive esters in aqueous systems is often used in bioconjugation chemistry, but it must compete against hydrolysis processes. Here we study the kinetics of aminolysis and hydrolysis of 2-S-phosphorylacetate ester intermediates that result from displacement of bromide by a thiophosphate nucleophile from commonly used bromoacetate ester cross-linking agents. Results: We found cross-linking between uridine-5′-monophosphorothioate and D-glucosamine using N-hydroxybenzotriazole and N-hydroxysuccinimde bromoacetates to be ineffective. In order to gain insight into these shortfalls, 2-S-(5′-thiophosphoryluridine)acetic acid esters were prepared using p-nitrophenyl bromoacetate or m-nitrophenyl bromoacetate in combination with uridine-5′-monophosphorothioate. Kinetics of hydrolysis and aminolysis of the resulting p- and m-nitrophenyl 2-S-(5′-thiophosphoryluridine)acetates were determined by monitoring the formation of phenolate ions spectrophotometrically as a function of pH. The p- and m-nitrophenyl 2-S-(5′-thiophosphoryluridine)acetates showed similar reactivity profiles despite the significant difference in the pK aH values of their nitrophenolate leaving groups. Both were more reactive with respect to hydrolysis and aminolysis in comparison to their simple acetate progenitors, but their calculated selectivity towards aminolysis vs hydrolysis, while reasonable, would not lead to clean reactions that do not require purification. Extrapolations of the kinetic data were used to predict leaving group pK a values that could lead to improved selectivity towards aminolysis while retaining reasonable reaction times. Conclusions: Both p- and m-nitrophenyl 2-S-(5′-thiophosphoryluridine)acetates show some selectivity towards aminolysis over hydrolysis, with the m-nitrophenolate system displaying slightly better selectivity. Extrapolation of the data for hydrolysis and aminolysis of these esters suggests that the use of readily accessible trifluoroethyl 2-S-(5′-thiophosphoryluridine)acetate with a leaving group pK aH of 12.4 should afford better selectivity while maintaining reasonable reaction times. Kinetically, p- and m-nitrophenyl 2-S-(5′-thiophosphoryluridine)acetates show similar properties to o-nitrophenyl 2-S-ethylacetate, and show no evidence for intramolecular catalysis of hydrolysis or aminolysis by the phosphoryl groups.

scholarly journals Crystal structure of the dopamine N-acetyltransferase–acetyl-CoA complex provides insights into the catalytic mechanism

2012 ◽  
Vol 446 (3) ◽  
pp. 395-404 ◽  
Author(s):  
Kuo-Chang Cheng ◽  
Jhen-Ni Liao ◽  
Ping-Chiang Lyu
Keyword(s):  
Crystal Structure ◽  
Catalytic Mechanism ◽  
Complex Structure ◽  
Kinetic Studies ◽  
Catalytic Triad ◽  
Site Directed Mutagenesis ◽  
Structural Basis ◽  
Titration Calorimetry ◽  
Acetyl Coa ◽  
Acetyl Transfer

The daily cycle of melatonin biosynthesis in mammals is regulated by AANAT (arylalkylamine N-acetyltransferase; EC 2.3.1.87), making it an attractive target for therapeutic control of abnormal melatonin production in mood and sleep disorders. Drosophila melanogaster Dat (dopamine N-acetyltransferase) is an AANAT. Until the present study, no insect Dat structure had been solved, and, consequently, the structural basis for its acetyl-transfer activity was not well understood. We report in the present paper the high-resolution crystal structure for a D. melanogaster Dat–AcCoA (acetyl-CoA) complex obtained using one-edge (selenium) single-wavelength anomalous diffraction. A binding study using isothermal titration calorimetry suggested that the cofactor bound to Dat first before substrate. Examination of the complex structure and a substrate-docked model indicated that Dat contains a novel AANAT catalytic triad. Site-directed mutagenesis, kinetic studies and pH-rate profiles confirmed that Glu47, Ser182 and Ser186 were critical for catalysis. Collectively, the results of the present study suggest that Dat possesses a specialized active site structure dedicated to a catalytic mechanism.

scholarly journals Kinetic Studies of Cs+ and Sr2+ Ion Exchange Using Clinoptilolite in Static Columns and an Agitated Tubular Reactor (ATR)

2021 ◽  
Vol 5 (1) ◽  
pp. 9
Author(s):  
Muhammad Yusuf Prajitno ◽  
Mohamad Taufiqurrakhman ◽  
David Harbottle ◽  
Timothy N. Hunter
Keyword(s):  
Adsorption Capacity ◽  
Tubular Reactor ◽  
Process Intensification ◽  
Kinetic Studies ◽  
Breakthrough Curves ◽  
Maximum Adsorption Capacity ◽  
Batch Studies ◽  
Shear Mixing ◽  
Natural Clinoptilolite ◽  
Kinetics Of

Natural clinoptilolite was studied to assess its performance in removing caesium and strontium ions, using both static columns and an agitated tube reactor (ATR) for process intensification. Kinetic breakthrough curves were fitted using the Thomas and Modified Dose Response (MDR) models. In the static columns, the clinoptilolite adsorption capacity (qe) for 200 ppm ion concentrations was found to be ~171 and 16 mg/g for caesium and strontium, respectively, highlighting the poor material ability to exchange strontium. Reducing the concentration of strontium to 100 ppm, however, led to a higher strontium qe of ~48 mg/g (close to the maximum adsorption capacity). Conversely, halving the column residence time to 15 min decreased the qe for 100 ppm strontium solutions to 13–14 mg/g. All the kinetic breakthrough data correlated well with the maximum adsorption capacities found in previous batch studies, where, in particular, the influence of concentration on the slow uptake kinetics of strontium was evidenced. For the ATR studies, two column lengths were investigated (of 25 and 34 cm) with the clinoptilolite embedded directly into the agitator bar. The 34 cm-length system significantly outperformed the static vertical columns, where the adsorption capacity and breakthrough time were enhanced by ~30%, which was assumed to be due to the heightened kinetics from shear mixing. Critically, the increase in performance was achieved with a relative process flow rate over twice that of the static columns.

scholarly journals Biochar Chemistry in a Weathered Tropical Soil: Kinetics of Phosphorus Sorption

Agriculture ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 295
Author(s):  
Marina Moura Morales ◽  
Nicholas Brian Comerford ◽  
Maurel Behling ◽  
Daniel Carneiro de Abreu ◽  
Iraê Amaral Guerrini
Keyword(s):  
Mineral Soil ◽  
Soil Surface ◽  
Kinetic Studies ◽  
Inorganic Phosphorus ◽  
Initial Reaction ◽  
Phosphorus Sorption ◽  
P Sorption ◽  
Published Research ◽  
Kinetics Of

The phosphorus (P) chemistry of biochar (BC)-amended soils is poorly understood. This statement is based on the lack of published research attempting a comprehensive characterization of biochar’s influence on P sorption. Therefore, this study addressed the kinetic limitations of these processes. This was accomplished using a fast pyrolysis biochar made from a mix of waste materials applied to a highly weathered Latossolo Vermelho distrofico (Oxisol) from São Paulo, Brazil. Standard method (batch method) was used. The sorption kinetic studies indicated that P sorption in both cases, soil (S) and soil-biochar (SBC), had a relatively fast initial reaction between 0 to 5 min. This may have happened because adding biochar to the soil decreased P sorption capacity compared to the mineral soil alone. Presumably, this is a result of: (i) Inorganic phosphorus desorbed from biochar was resorbed onto the mineral soil; (ii) charcoal particles physically covered P sorption locations on soil; or (iii) the pH increased when BC was added SBC and the soil surface became more negatively charged, thus increasing anion repulsion and decreasing P sorption.

INHOMOGENEOUS LARGE DEFORMATION KINETICS OF POLYMERIC GELS

2013 ◽  
Vol 05 (01) ◽  
pp. 1350001 ◽  
Author(s):  
WILLIAM TOH ◽  
ZISHUN LIU ◽  
TENG YONG NG ◽  
WEI HONG
Keyword(s):  
Large Deformation ◽  
Soft Matter ◽  
Inner Core ◽  
Kinetic Studies ◽  
Fe Model ◽  
One Dimensional ◽  
Simplified Approach ◽  
Deformation Kinetics ◽  
Polymeric Gels ◽  
Kinetics Of

This work examines the dynamics of nonlinear large deformation of polymeric gels, and the kinetics of gel deformation is carried out through the coupling of existing hyperelastic theory for gels with kinetic laws for diffusion of small molecules. As finite element (FE) models for the transient swelling process is not available in commercial FE software, we develop a customized FE model/methodology which can be used to simulate the transient swelling process of hydrogels. The method is based on the similarity between diffusion and heat transfer laws by determining the equivalent thermal properties for gel kinetics. Several numerical examples are investigated to explore the capabilities of the present FE model, namely: a cube to study free swelling; one-dimensional constrained swelling; a rectangular block fixed to a rigid substrate to study swelling under external constraints; and a thin annulus fixed at the inner core to study buckling phenomena. The simulation results for the constrained block and one-dimensional constrained swelling are compared with available experimental data, and these comparisons show a good degree of similarity. In addition to this work providing a valuable tool to researchers for the study of gel kinetic deformation in the various applications of soft matter, we also hope to inspire works to adopt this simplified approach, in particular to kinetic studies of diffusion-driven mechanisms.

scholarly journals Hydrogen peroxide‐mediated conversion of coproheme to heme b by HemQ—lessons from the first crystal structure and kinetic studies

FEBS Journal ◽  
2016 ◽  
Vol 283 (23) ◽  
pp. 4386-4401 ◽  
Author(s):  
Stefan Hofbauer ◽  
Georg Mlynek ◽  
Lisa Milazzo ◽  
Dominic Pühringer ◽  
Daniel Maresch ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Hydrogen Peroxide ◽  
Kinetic Studies

Alkene Difunctionalization Directed by Free Amines: Diamine Synthesis via Nickel-Catalyzed 1,2-Carboamination

2021 ◽  
Author(s):  
Taeho Kang ◽  
José Manuel González ◽  
Zi-Qi Li ◽  
Klement Foo ◽  
Peter Cheng ◽  
...  
Keyword(s):  
Nickel Catalyst ◽  
Room Temperature ◽  
Kinetic Studies ◽  
Fine Tuning ◽  
Secondary Amines ◽  
Protecting Group ◽  
Wide Range ◽  
Leaving Group ◽  
Primary And Secondary Amines ◽  
Reaction Proceeds

A versatile method to access differentially substituted 1,3- and 1,4-diamines via a nickel-catalyzed three-component 1,2-carboamination of alkenyl amines with aryl/alkenylboronic ester nucleophiles and N–O electrophiles is reported. The reaction proceeds efficiently with free primary and secondary amines without needing a directing auxiliary or protecting group, and is enabled by fine-tuning the leaving group on the N–O reagent. The transformation is highly regioselective and compatible with a wide range of coupling partners and alkenyl amine substrates, all performed at room temperature. A series of kinetic studies support a mechanism in which alkene coordination to the nickel catalyst is turnover-limiting.

Sign in / Sign up

Export Citation Format

Share Document