scholarly journals Differences between the electric fields of the catalytic sites of papain and actinidin detected by using the thiol-located nitrobenzofurazan label as a spectroscopic reporter group

1984 ◽  
Vol 220 (2) ◽  
pp. 609-612 ◽  
Author(s):  
K Brocklehurst ◽  
E Salih ◽  
T S Lodwig
Keyword(s):  
Electric Fields ◽  
Electronic Absorption Spectra ◽  
Catalytic Site ◽  
X Ray Diffraction ◽  
Guanidinium Chloride ◽  
Dependent Change ◽  
Catalytic Sites ◽  
Ph Dependent ◽  
Ph Range ◽  
Reporter Group

The catalytic-site thiol groups of papain (EC 3.4.22.2) and actinidin (EC 3.4.22.14) were each labelled with the nitrobenzofurazan (Nbf) chromophore by reaction with 4-chloro-7-nitrobenzofurazan at pH 4.4. The electronic-absorption spectra of both labelled enzymes were determined in aqueous solution, in the pH ranges approx. 2-5 for S-Nbf-papain and approx. 3.3-8 for S-Nbf-actinidin, and for the latter also in 6 M-guanidinium chloride. The spectrum of S-Nbf-papain is characterized by lambda max. = 402 nm at pH 5 and by lambda max. = 422 nm at pH 2.18. The pH-dependent shift in lambda max. accompanies a pH-dependent change in A 430, the nature of which is consistent with its dependence on a single ionizing group with pKa 3.7. The spectrum of S-Nbf-actinidin is pH-independent in the pH range approx. 3.3-8 and is characterized by lambda max. = 413 nm. This absorption maximum shifts to 425 nm in 6M-guanidinium chloride. These results are discussed and related to those reported previously from studies on papain and actinidin with various reactivity probes. Despite the close similarity in the catalytic sites of papain and actinidin deduced from X-ray-diffraction studies, the considerable differences in their reactivity characteristics are mirrored by differences in their electric fields detected by the Nbf spectroscopic label. The microenvironment in the catalytic site of actinidin appears to favour the existence of ions significantly more than in the corresponding region in papain.

pH-Dependent Thermal Stability of Vibrio cholerae L-asparaginase

2019 ◽  
Vol 26 (10) ◽  
pp. 743-750 ◽  
Author(s):  
Remya Radha ◽  
Sathyanarayana N. Gummadi
Keyword(s):  
Vibrio Cholerae ◽  
Conformational Changes ◽  
Kinetic Studies ◽  
Structural Features ◽  
Structure Stability ◽  
Kcal Mole ◽  
Scanning Calorimetry ◽  
Wide Range ◽  
Ph Dependent ◽  
Ph Range

Background:pH is one of the decisive macromolecular properties of proteins that significantly affects enzyme structure, stability and reaction rate. Change in pH may protonate or deprotonate the side group of aminoacid residues in the protein, thereby resulting in changes in chemical and structural features. Hence studies on the kinetics of enzyme deactivation by pH are important for assessing the bio-functionality of industrial enzymes. L-asparaginase is one such important enzyme that has potent applications in cancer therapy and food industry.Objective:The objective of the study is to understand and analyze the influence of pH on deactivation and stability of Vibrio cholerae L-asparaginase.Methods:Kinetic studies were conducted to analyze the effect of pH on stability and deactivation of Vibrio cholerae L-asparaginase. Circular Dichroism (CD) and Differential Scanning Calorimetry (DSC) studies have been carried out to understand the pH-dependent conformational changes in the secondary structure of V. cholerae L-asparaginase.Results:The enzyme was found to be least stable at extreme acidic conditions (pH< 4.5) and exhibited a gradual increase in melting temperature from 40 to 81 °C within pH range of 4.0 to 7.0. Thermodynamic properties of protein were estimated and at pH 7.0 the protein exhibited ΔG37of 26.31 kcal mole-1, ΔH of 204.27 kcal mole-1 and ΔS of 574.06 cal mole-1 K-1.Conclusion:The stability and thermodynamic analysis revealed that V. cholerae L-asparaginase was highly stable over a wide range of pH, with the highest stability in the pH range of 5.0–7.0.

Effect of Deacetylation on Characterization of pH Stimulus Responsive Chitosan-Acrylamide Hydrogels Using Radiation

2014 ◽  
Vol 896 ◽  
pp. 292-295 ◽  
Author(s):  
Kris Tri Basuki ◽  
Deni Swantomo ◽  
Sigit ◽  
Kartini Megasari
Keyword(s):  
Electric Fields ◽  
Chemical Sensor ◽  
Graft Copolymerization ◽  
X Ray Diffraction ◽  
Grafting Efficiency ◽  
Sensor Material ◽  
Swelling Degree ◽  
Gel Fraction ◽  
Stimulus Responsive ◽  
Acetyl Group

Smart hydrogels which can change their swelling behavior and other properties in response to environmental stimuli such as temperature, pH, solvent composition and electric fields, have attracted great interest as chemical sensor material and controlled release system. The pH stimulus responsive hydrogels were synthesized by gamma-irradiation graft copolymerization of chitosan-acrylamide. In this research the influence of deacetylation process on the hydrogels characterization were investigated by measuring grafting efficiency, gel fraction, swelling degree, and crosslink density. Evidence of grafting was confirmed by FTIR spectroscopy. X-ray diffraction showed reduction in the crystallinity of chitosan with different deacetylation process also after the graft copolymerization reaction. The results showed that decreasing acetyl group of chitosan increase the grafting efficiency, gel fraction and swelling degree. While crystallinity decreased. The hydrogels indicated pH-dependent swelling behaviour.

scholarly journals Non-protein components of the cell surface of Staphylococcus aureus

1968 ◽  
Vol 107 (6) ◽  
pp. 817-821 ◽  
Author(s):  
A. M. James ◽  
J. E. Brewer
Keyword(s):  
Staphylococcus Aureus ◽  
Cell Surface ◽  
Teichoic Acid ◽  
Surface Damage ◽  
Sodium Metaperiodate ◽  
Maximum Value ◽  
Dependent Change ◽  
Ph Dependent ◽  
Pass Through ◽  
Protein Components

1. pH–mobility curves of various laboratory strains of Staphylococcus aureus are non-sigmoid in shape, and all pass through a maximum value in the range pH4–5. 2. The maxima in the curves are not due to incomplete washing of the cells, adsorption of buffer components or irreversible surface damage. 3. Mild oxidation of the cell-surface teichoic acid with sodium metaperiodate gives cells that have typical sigmoid pH–mobility curves, characteristic of either a simple carboxyl surface or a mixed carboxyl–amino surface. 4. The results are discussed in terms of a pH-dependent change in the configuration of the teichoic acid molecules at the surface.

Use of bentonite to control the release of copper from contaminated soils

Soil Research ◽  
2007 ◽  
Vol 45 (8) ◽  
pp. 618 ◽  
Author(s):  
Wanting Ling ◽  
Qing Shen ◽  
Yanzheng Gao ◽  
Xiaohong Gu ◽  
Zhipeng Yang
Keyword(s):  
Heavy Metals ◽  
Sorption Capacity ◽  
Contaminated Soils ◽  
Montmorillonite Clay ◽  
Maximum Sorption Capacity ◽  
Maximum Sorption ◽  
Wide Ph Range ◽  
Ph Dependent ◽  
Ph Range ◽  
Soil Ageing

A decrease in release and availability of heavy metals in soil has been of worldwide interest in recent years. Bentonite is a type of expandable montmorillonite clay, and has strong sorption for heavy metals. In this work, the control of amended bentonite on the release of copper (Cu2+) from spiked soils was investigated using a batch equilibrium technique. Sorption of Cu by bentonite was pH-dependent, and could be well described using the Langmiur model. Maximum sorption capacity of the bentonite used in this study was 5.4 mg/g, which was much greater than soils reported in the literature. The extent of Cu2+ release from spiked soils was correlated with slurry concentrations, pH, and soil ageing process. In all cases, the amendment of bentonite was observed to effectively decrease the release of Cu2+ from soils. The apparent aqueous concentrations of Cu2+ released from soils devoid of bentonite treatment were 113–1160% higher than those from the soils amended with bentonite. Moreover, the magnitude of Cu2+ release decreased with increasing amount of bentonite added to soils. The bentonite added was more effective in retaining Cu2+ in sorbents for aged contaminated soils. Such enhanced retention resulting from the presence of bentonite was observed within a wide pH range from 2.5 to 7.0. Bentonite, as one of the most abundant minerals in soils, is regarded to improve the soil overall quality. The results obtained from this work provide useful information on utilisation of bentonite to control the release of heavy metals from contaminated soils.

scholarly journals Human insulin polymorphism upon ligand binding and pH variation: the case of 4-ethylresorcinol

IUCrJ ◽  
2015 ◽  
Vol 2 (5) ◽  
pp. 534-544 ◽  
Author(s):  
S. Fili ◽  
A. Valmas ◽  
M. Norrman ◽  
G. Schluckebier ◽  
D. Beckers ◽  
...  
Keyword(s):  
Human Insulin ◽  
Organic Ligand ◽  
European Synchrotron Radiation Facility ◽  
X Ray Diffraction ◽  
Ph Variation ◽  
X Ray ◽  
X Ray Crystallography ◽  
Swiss Light Source ◽  
Crystallization Experiments ◽  
Ph Range

This study focuses on the effects of the organic ligand 4-ethylresorcinol on the crystal structure of human insulin using powder X-ray crystallography. For this purpose, systematic crystallization experiments have been conducted in the presence of the organic ligand and zinc ions within the pH range 4.50–8.20, while observing crystallization behaviour around the isoelectric point of insulin. High-throughput crystal screening was performed using a laboratory X-ray diffraction system. The most representative samples were selected for synchrotron X-ray diffraction measurements, which took place at the European Synchrotron Radiation Facility (ESRF) and the Swiss Light Source (SLS). Four different crystalline polymorphs have been identified. Among these, two new phases with monoclinic symmetry have been found, which are targets for the future development of microcrystalline insulin drugs.

Syntheses and crystal structures of guanidine hydrochlorides with two Schiff base functions as efficient colorimetric and selective sensors for fluoride

2018 ◽  
Vol 73 (8) ◽  
pp. 601-609 ◽  
Author(s):  
Bei Wang ◽  
Pei-Zhi Zhang ◽  
Xin Chen ◽  
Ai-Quan Jia ◽  
Qian-Feng Zhang
Keyword(s):  
Optical Properties ◽  
Schiff Base ◽  
Molecular Structures ◽  
X Ray Diffraction ◽  
Guanidinium Chloride ◽  
Visible Absorption ◽  
X Ray ◽  
Color Changes ◽  
Base Functions ◽  
Magnetic Resonances

AbstractA series of guanidinium chloride derivatives have been synthesized by condensation of 1,3-diaminoguanidine monohydrochloride with heteroaromatic formaldehydes in good yields. All compounds were characterized by nuclear magnetic resonances and infrared spectroscopies, and the molecular structures of four compounds were determined by single crystal X-ray diffraction. The optical properties of these guanidinium chloride derivatives with fluoride anions were investigated, showing selective color changes from colorless to yellow or orange, red-shifted in the ultraviolet/visible absorption spectra.

Oxidation of Nickel(II) and Manganese(II) by Peroxodisulfate in Aqueous Solution in the Presence of Molybdate. Crystal Structure of the (NH4)6[NiMo9O32].6H2O Product

1992 ◽  
Vol 45 (12) ◽  
pp. 1943 ◽  
Author(s):  
SJ Dunne ◽  
RC Burns ◽  
GA Lawrance
Keyword(s):  
Rate Constant ◽  
Linear Dependence ◽  
Ph Dependence ◽  
Order Rate Constant ◽  
X Ray Diffraction ◽  
X Ray ◽  
First Order ◽  
Oxidant Concentration ◽  
Ph Range ◽  
Kinetics Of

Oxidation of Ni2+,aq, by S2O82- to nickel(IV) in the presence of molybdate ion, as in the analogous manganese system, involves the formation of the soluble heteropolymolybdate anion [MMogO32]2- (M = Ni, Mn ). The nickel(IV) product crystallized as (NH4)6 [NiMogO32].6H2O from the reaction mixture in the rhombohedra1 space group R3, a 15.922(1), c 12.406(1) � ; the structure was determined by X-ray diffraction methods, and refined to a residual of 0.025 for 1741 independent 'observed' reflections. The kinetics of the oxidation were examined at 80 C over the pH range 3.0-5.2; a linear dependence on [S2O82-] and a non-linear dependence on l/[H+] were observed. The influence of variation of the Ni/Mo ratio between 1:10 and 1:25 on the observed rate constant was very small at pH 4.5, a result supporting the view that the precursor exists as the known [NiMo6O24H6]4- or a close analogue in solution. The pH dependence of the observed rate constant at a fixed oxidant concentration (0.025 mol dm-3) fits dequately to the expression kobs = kH [H+]/(Ka+[H+]) where kH = 0.0013 dm3 mol-1 s-1 and Ka = 4-0x10-5. The first-order dependence on peroxodisulfate subsequently yields a second-order rate constant of 0.042 dm3 mol-1 s-1. Under analogous conditions, oxidation of manganese(II) occurs eightfold more slowly than oxidation of nickel(II), whereas oxidation of manganese(II) by peroxomonosulfuric acid is 16-fold faster than oxidation by peroxodisulfate under similar conditions.

scholarly journals Large-area printing of ferroelectric surface and super-domains for efficient solar water splitting

2020 ◽  
Author(s):  
Yu Tian ◽  
Yaqing Wei ◽  
Minghui Pei ◽  
Rongrong Cao ◽  
Zhenao Gu ◽  
...  
Keyword(s):  
Water Splitting ◽  
Electric Fields ◽  
Electronic Structures ◽  
Active Sites ◽  
Large Area ◽  
Solar Water Splitting ◽  
High Efficient ◽  
Catalytic Sites ◽  
Order Of Magnitude ◽  
Magnitude Increase

Abstract Surface electronic structures of the photoelectrodes determine the activity and efficiency of the photoelectrochemical water splitting, but the controls of their surface structures and interfacial chemical reactions remain challenging. Here, we use ferroelectric BiFeO3 as a model system to demonstrate an efficient and controllable water splitting reaction by large-area constructing the hydroxyls-bonded surface. The up-shift of band edge positions at this surface enables and enhances the interfacial holes and electrons transfer through the hydroxyl-active-sites, leading to simultaneously enhanced oxygen and hydrogen evolutions. Furthermore, printing of ferroelectric super-domains with microscale checkboard up/down electric fields separates the distribution of reduction/oxidation catalytic sites, enhancing the charge separation and giving rise to an order of magnitude increase of the photocurrent. This large-area printable ferroelectric surface and super-domains offer an alternative platform for controllable and high-efficient photocatalysis.

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