Mechanism-based inactivation of gastric peroxidase by mercaptomethylimidazole

The mechanism of inhibition of gastric peroxidase (GPO) activity by mercaptomethylimidazole (MMI), an inducer of gastric acid secretion, has been investigated. Incubation of purified GPO with MMI in the presence of H2O2 results in irreversible inactivation of the enzyme. No significant inactivation occurs in the absence of H2O2 or MMI, suggesting the involvement of peroxidase-catalysed oxidized MMI (MMIOX.) in the inactivation process. The inactivation follows pseudo-first-order kinetics consistent with a mechanism-based (suicide) mode. The pseudo-first-order kinetic constants at pH 8 are ki = 111 microM, k(inact.) = 0.55 min-1 and t1/2 = 1.25 min, and the second-order rate constant is 0.53 x 10(4) M-1 x min-1. Propylthiouracil also inactivates GPO activity in the same manner but its efficiency (k(inact./ki = 0.46 mM-1 x min-1) is about 10 times lower than that of MMI (k(inact./ki = 5 mM-1 x min-1). The rate of inactivation with MMI shows pH-dependence with an inflection point at 7.3, indicating the involvement in the inactivation process of an ionizable group on the enzyme with a pKa of 7.3. The enzyme is remarkably protected against inactivation by micromolar concentrations of electron donors such as iodide and bromide but not by chloride. Although GPO oxidizes MMI slowly, iodide stimulates it through enzymic generation of I+ which is reduced back to I- by MMI. Although MMIOX. is formed at a much higher rate in the presence of I-, a constant concentration of I- maintained via the reduction of I+ by MMI, protects the active site of the enzyme against inactivation. We suggest that MMI inactivates catalytically active GPO by acting as a suicidal substrate.

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A Highly Efficient Ag Nanoparticle-Immobilized Alginate-g-Polyacrylonitrile Hybrid Photocatalyst for the Degradation of Nitrophenols

Polymers ◽

10.3390/polym12123049 ◽

2020 ◽

Vol 12 (12) ◽

pp. 3049

Author(s):

Imran Hasan ◽

Charu Shekhar ◽

Walaa Alharbi ◽

Maymonah Abu Khanjer ◽

Rais Ahmad Khan ◽

...

Keyword(s):

Irradiation Time ◽

Analytical Techniques ◽

Order Rate Constant ◽

Order Kinetic ◽

Ag Nps ◽

Reaction Conditions ◽

First Order ◽

Order Kinetic Model ◽

Pseudo First Order

Herein, we report PAN-g-Alg@Ag-based nanocatalysts synthesis via in situ oxidative free-radical polymerization of acrylonitrile (AN) using Alg@Ag nanoparticles (Alg@Ag NPs). Various analytical techniques, including FTIR, XRD, SEM, TEM, UV–Vis, and DSC, were employed to determine bonding interactions and chemical characteristics of the nanocatalyst. The optimized response surface methodology coupled central composite design (RSM–CCD) reaction conditions were a 35-min irradiation time in a 70-mg L−1 2,4-dinitrophenol (DNP) solution at pH of 4.68. Here, DNP degradation was 99.46% at a desirability of 1.00. The pseudo-first-order rate constant (K1) values were 0.047, 0.050, 0.054, 0.056, 0.059, and 0.064 min−1 with associated half-life (t1/2) values of 14.74, 13.86, 12.84, 12.38, 11.74, 10.82, and 10.04 min that corresponded to DNP concentrations of 10, 20, 30, 40, 50, 60, and 70 mg L−1, respectively, in the presence of PAN-g-Alg@Ag (0.03 g). The results indicate that the reaction followed the pseudo-first-order kinetic model with an R2 value of 0.99. The combined absorption properties of PAN and Alg@Ag NPs on copolymerization on the surface contributed more charge density to surface plasmon resonance (SPR) in a way to degrade more and more molecules of DNP together with preventing the recombination of electron and hole pairs within the photocatalytic process.

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Kinetics of diatrizoate degradation by ozone and the formation of disinfection by-products in the sequential chlorination

Journal of Water Reuse and Desalination ◽

10.2166/wrd.2021.053 ◽

2021 ◽

Author(s):

Chen-Yan Hu ◽

Si-Cheng Ren ◽

Yi-Li Lin ◽

Ji-Chen Zhang ◽

Ye-Ye Zhu ◽

...

Keyword(s):

Ozone Concentration ◽

Ph Value ◽

Degradation Kinetics ◽

Order Rate Constant ◽

Order Kinetic ◽

Solution Ph ◽

First Order ◽

Pseudo First Order ◽

Kinetics Of ◽

By Products

Abstract In this study, we studied the degradation kinetics of a common iodine contrast agent, diatrizoate, by ozone and the formation of disinfection by-products (DBPs) in the sequential chlorination. Effects of ozone concentration, solution pH, and bromide concentration on diatrizoate degradation were evaluated. The results indicate that diatrizoate can be effectively degraded (over 80% within 1 h) by ozone, and the degradation kinetics can be well described using the pseudo-first-order kinetic model. The pseudo-first-order rate constant (kobs) of diatrizoate degradation significantly increased with increasing ozone concentration and decreasing bromide concentration. The kobs kept increasing with the increase of pH value and reached a maximum of 6.5 (±0.05) × 10−2 min−1 at pH 9. As the ozone concentration gradually increased from 0.342 to 1.316 mg/L, the corresponding kobs of diatrizoate degradation increased from 1.76 (±0.20) × 10−3 to 4.22 (±0.3) × 10−2 min−1. The bromide concentration exhibited a strong inhibitory effect on diatrizoate degradation because of the competition for ozone with diatrizoate. Trichloromethane was the only detected DBP in the subsequent chlorination in the absence of bromide. However, in the presence of bromide, six other DBPs were detected, and bromochloroiodomethane and tribromomethane became the major products with concentrations 1–2 orders higher than those of the other DBPs. In order to provide safe drinking water to the public, water should be maintained at circumneutral pH values and low bromine concentrations (<5 μM) before reaching the chlorine disinfection process to effectively control the formation of DBPs.

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Oxidation of the mercurous ion by peroxidase

Canadian Journal of Chemistry ◽

10.1139/v86-162 ◽

1986 ◽

Vol 64 (5) ◽

pp. 969-972 ◽

Cited By ~ 1

Author(s):

Donald C. Wigfield ◽

Season Tse

Keyword(s):

Elemental Mercury ◽

Order Rate Constant ◽

Kinetics Of Oxidation ◽

First Order ◽

Order Rate ◽

First Order Kinetics ◽

Cold Vapour ◽

Pseudo First Order ◽

Kinetics Of ◽

Mercurous Ion

The kinetics of oxidation of the mercurous ion by peroxidase have been measured by following the disappearance of mercurous ion using cold-vapour atomic absorption spectroscopy. Pseudo-first-order kinetics are observed with respect to mercurous ion, and the pseudo-first-order rate constants are linearly related to peroxidase concentration, showing first-order dependence on peroxidase. This behaviour is identical to oxidation of elemental mercury, and the second-order rate constant, 1.44 × 104 M−1 s−1 at 23 °C, is also, within experimental error, the same as that for elemental mercury oxidation. The data are interpreted in terms of peroxidase-induced disproportionation of the mercurous dimer, followed by two-electron oxidation of zero-valent mercury.

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Active-site-directed inactivation of Schizophyllum commune cellulase by 4′, 5′-epoxypentyl-4-D-(β-D-glucopyranosyl)-β-D-glucopyranoside

Biochemistry and Cell Biology ◽

10.1139/o88-099 ◽

1988 ◽

Vol 66 (8) ◽

pp. 871-879 ◽

Cited By ~ 6

Author(s):

Anthony John Clarke

Keyword(s):

Active Site ◽

Schizophyllum Commune ◽

Competitive Inhibitor ◽

Irreversible Inhibitor ◽

Inhibitor Molecule ◽

Enzyme Active Site ◽

First Order ◽

First Order Kinetics ◽

Pseudo First Order ◽

Inactivation Process

4′,5′-Epoxypentyl-4-D-(β-D-glucopyranosyl)-β-D-glucopyranoside (4) was synthesized by a Koenigs–Knorr reaction of 4-penten-1-ol and acetobromcellobiose, promoted by silver trifluoromethanesulfonate and N,N′-tetramethylurea, and tested as a potential active-site-directed irreversible inhibitor of the Schizophyllum commune cellulase. Incubation of the S. commune cellulase with 4 resulted in a time-dependent irreversible inactivation of the enzyme. The inactivation process obeyed pseudo-first-order kinetics and the hyperbolic plot of kobs as a function of inhibitor concentration provided values for Kd and k2 of 150 mM and 2.0 × 10−4 s−1, respectively, at pH 5.5 and 25 °C. The binding of a competitive inhibitor, cellobiose, to the cellulase prior to incubation with 4 protected the enzyme from rapid inactivation, suggesting that the inactivation is due to attack at the active site. The dependence of the inactivation on pH is consistent with the participation of carboxyl groups. Treatment of the affinity-labeled enzyme with [14C]methoxyamine resulted in the near stoichiometric formation of a stable radiolabelled adduct, suggesting that one inhibitor molecule binds per enzyme active site of the enzyme.

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U(VI) adsorption in water by sodium alginate modified Bacillus megaterium

Royal Society Open Science ◽

10.1098/rsos.202098 ◽

2021 ◽

Vol 8 (2) ◽

Author(s):

Dianxin Li ◽

Yiqing Yang ◽

Peng Zhang ◽

Jiangang Liu ◽

Tao Li ◽

...

Keyword(s):

Adsorption Capacity ◽

Sodium Alginate ◽

Bacillus Megaterium ◽

Adsorption Process ◽

Batch Adsorption ◽

Maximum Adsorption Capacity ◽

Order Kinetic ◽

First Order ◽

First Order Kinetics ◽

Pseudo First Order

The surface of Bacillus megaterium was modified by coating sodium alginate. The modified B. megaterium before and after adsorption were characterized by SEM, FTIR and XPS. The effects of pH, reaction time, initial U(VI) concentration and adsorbent dosage on the adsorption of U(VI) by the modified B. megaterium were studied by batch adsorption experiments. The adsorption process was studied by pseudo-first-order kinetics and pseudo-second-order kinetic models, Langmuir and Freundlich isotherms. The results showed that the maximum adsorption capacity of U(VI) was 74.61 mg g −1 under the conditions of pH 5.0, adsorbent 0.2 g l −1 , 30°C and initial U(VI) concentration of 15 mg l −1 . The adsorption process accords with pseudo-first-order kinetics and Langmuir isotherm. The adsorption capacity of U(VI) by the modified B. megaterium was still higher than 80% after five times of desorption and reuse experiments. In conclusion, the sodium alginate modified B. megaterium was an ideal material for U(VI) biosorption.

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Iron Supported on Ion Exchange Resin as Source of Iron for Fenton Reagent: A Heterogeneous or a Homogeneous Fenton Reagent Generation?

International Journal of Chemical Reactor Engineering ◽

10.1515/ijcre-2017-0026 ◽

2017 ◽

Vol 15 (5) ◽

Cited By ~ 3

Author(s):

Orlando García-Rodríguez ◽

Jennifer A. Bañuelos ◽

Luis A. Godínez ◽

Hortencia C. Arredondo Valdez ◽

Evelyn Zamudio ◽

...

Keyword(s):

Ion Exchange ◽

Exchange Resin ◽

Dye Decolorization ◽

Ion Exchange Resin ◽

Order Kinetic ◽

Fenton Reagent ◽

First Order ◽

Relative Contribution ◽

First Order Kinetics ◽

Pseudo First Order

Abstract The aim of this work is to discuss the relative contribution of homogeneous and heterogeneous Fenton processes in the treatment of Orange II dye solutions at pH 3 and 7 using an ion exchange resin as iron support. While at pH 3, 99% of the colour was removed, under neutral conditions a decoloration of 56% was observed. Studying the release of iron from the resin, we found a concentration of 1.49 mg/L of ferric ion and 0.31 mg/L of ferrous ion at pH 3 and 1.08 mg/L and 0.11 mg/L at pH 7, revealing that as expected, dissolution of iron ions at pH 3 is larger. Using these concentrations in a homogeneous process, 45% of the colour can be removed at pH 3 and 10% at pH 7, so it was infered that there is an effect of the iron that is still supported on the resin. In this way, a mixed homogeneous/heterogeneous mechanism could be proposed. While the experimental data for the desorption of iron at pH 3 was well suited to a pseudo second order kinetic model, the desorption of iron at pH 7 was fit to pseudo-first order kinetics. Experimental results of dye decolorization were on the other hand, fitted to a pseudo first order kinetics.

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In-vitro Kinetic Hydrolysis Study of Metronidazole Derivatives with Carvacrol and Eugenol Using Validated RP-HPLC Method

Current Pharmaceutical Analysis ◽

10.2174/1573412916999200529123151 ◽

2020 ◽

Vol 16 ◽

Author(s):

M. Alarjah

Keyword(s):

Half Life ◽

Hplc Method ◽

Hydrolysis Rate ◽

First Order ◽

First Order Kinetics ◽

Rp Hplc ◽

Pharmacokinetic Properties ◽

Pseudo First Order ◽

Kinetic Hydrolysis

Background: Prodrugs principle is widely used to improve the pharmacological and pharmacokinetic properties of some active drugs. Much effort was made to develop metronidazole prodrugs to enhance antibacterial activity and or to improve pharmacokinetic properties of the molecule or to lower the adverse effects of metronidazole. Objective: In this work, the pharmacokinetic properties of some of monoterpenes and eugenol pro metronidazole molecules that were developed earlier were evaluated in-vitro. The kinetic hydrolysis rate constants and half-life time estimation of the new metronidazole derivatives were calculated using the validated RP-HPLC method. Method: Chromatographic analysis was done using Zorbbax Eclipse eXtra Dense Bonding (XDB)-C18 column of dimensions (250 mm, 4.6 mm, 5 μm), at ambient column temperature. The mobile phase was a mixture of sodium dihydrogen phosphate buffer of pH 4.5 and methanol in gradient elution, at 1ml/min flow rate. The method was fully validated according to the International Council for Harmonization (ICH) guidelines. The hydrolysis process carried out in an acidic buffer pH 1.2 and in an alkaline buffer pH 7.4 in a thermostatic bath at 37ºC. Results: The results followed pseudo-first-order kinetics. All metronidazole prodrugs were stable in the acidic pH, while they were hydrolysed in the alkaline buffer within a few hours (6-8 hr). The rate constant and half-life values were calculated, and their values were found to be 0.082- 0.117 hr-1 and 5.9- 8.5 hr., respectively. Conclusion: The developed method was accurate, sensitive, and selective for the prodrugs. For most of the prodrugs, the hydrolysis followed pseudo-first-order kinetics; the method might be utilised to conduct an in-vivo study for the metronidazole derivatives with monoterpenes and eugenol.

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Kinetics of bioactive compounds in functional spice Jiangpo during thermal processing

International Journal of Food Engineering ◽

10.1515/1556-3758.2768 ◽

2012 ◽

Vol 8 (3) ◽

Author(s):

Xiaoyan Dai ◽

Chenhuan Yu ◽

Qiaofeng Wu

Keyword(s):

Kinetic Parameters ◽

Bioactive Compounds ◽

Thermal Processing ◽

Order Rate Constant ◽

Heat Processing ◽

Order Kinetic ◽

Time Intervals ◽

First Order ◽

Order Kinetic Model ◽

Kinetics Of

Abstract Jiangpo is an increasingly popular East Asian spice which is made from Mangnolia officinalis bark and ginger juice. Since it induces bioactive compounds decomposition and has influence on final flavor and fragrance, cooking is regarded as the key operation in preparation of Jiangpo. To evaluate the bioactive compounds content changes of Jiangpo during thermal processing, kinetic parameters including reaction order, rate constant, T1/2 and activation energy of bioactive markers namely honokiol, magnolol and curcumin were determined. Cooking was set at temperatures 60, 90 and 120 °C for selected time intervals. Results displayed the thermal kinetic characteristics of the three compounds. Thermal degradation of Honokiol and magnolol both followed first order kinetic model and the loss of curcumin fitted second order. A mathematical model based on the obtained kinetic parameters has also been developed to predict the degradation of honokiol, magnolol and curcumin in non-isothermal state. All the information in this paper could contribute necessary information for optimizing the existing heat processing of Jiangpo.

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Ganglioside incorporation and release by the isolated perfused rat liver

Biochemical Journal ◽

10.1042/bj2740581 ◽

1991 ◽

Vol 274 (2) ◽

pp. 581-585 ◽

Cited By ~ 3

Author(s):

S C Kivatinitz ◽

A Miglio ◽

R Ghidoni

Keyword(s):

Rat Liver ◽

The Other ◽

Regulatory Role ◽

Isolated Perfused Rat Liver ◽

Order Kinetic ◽

Perfused Rat Liver ◽

Ganglioside Gm1 ◽

First Order ◽

Pseudo First Order

The fate of exogenous ganglioside GM1 labelled in the sphingosine moiety, [Sph-3H]GM1, administered as a pulse, in the isolated perfused rat liver was investigated. When a non-recirculating protocol was employed, the amount of radioactivity in the liver and perfusates was found to be dependent on the presence of BSA in the perfusion liquid and on the time elapsed after the administration of the ganglioside. When BSA was added to the perfusion liquid, less radioactivity was found in the liver and more in the perfusate at each time tested, for up to 1 h. The recovery of radioactivity in the perfusates followed a complex course which can be described by three pseudo-first-order kinetic constants. The constants, in order of decreasing velocity, are interpreted as: (a) the dilution of the labelled GM1 by the constant influx of perfusion liquid; (b) the washing off of GM1 loosely bound to the surface of liver cells; (c) the release of gangliosides from the liver. Process (b) was found to be faster in the presence of BSA, probably owing to the ability of BSA to bind gangliosides. The [Sph-3H]GM1 in the liver underwent metabolism, leading to the appearance of products of anabolic (GD1a, GD1b) and catabolic (GM2, GM3) origin; GD1a appeared before GM2 and GM3 but, at times longer than 10 min, GM2 and GM3 showed more radioactivity than GD1a. At a given time the distribution of the radioactivity in the perfusates was quite different from that of the liver. In fact, after 60 min GD1a was the only metabolite present in any amount, the other being GM3, the quantity of which was small. This indicates that the liver is able to release newly synthesized gangliosides quite specifically. When a recirculating protocol was used, there were more catabolites and less GD1a than with the non-recirculating protocol. A possible regulatory role of ganglioside re-internalization on their own metabolism in the liver is postulated.

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New insights on the UV/TiO2 photocatalytic treatment of thiomersal and its 2-sulfobenzoic acid product

Journal of Photocatalysis ◽

10.2174/2665976x02666210629104521 ◽

2021 ◽

Vol 02 ◽

Author(s):

Emmanuel M. de la Fournière ◽

Jorge M. Meichtry ◽

Graciela S. Custo ◽

Eduardo A. Gautier ◽

Marta I. Litter

Keyword(s):

Degradation Products ◽

Acidic Ph ◽

Cosmetic Products ◽

Acid Product ◽

First Order ◽

First Order Kinetics ◽

Photocatalytic Destruction ◽

Pseudo First Order ◽

Mineralization Degree ◽

Suitable Technique

Background: Thiomersal (TM), a complex between 2-mercaptobenzoic acid (2-MBA) and ethylmercury (C2H5Hg+), is an antimicrobial preservative used in immunological, ophthalmic, cosmetic products, and vaccines. Objective: TM has been treated by UV/TiO2 photocatalysis in the presence or absence of oxygen at acidic pH. C2H5Hg+, 2-MBA, and 2-sulfobenzoic acid (2-SBA) were found as products. A 2-SBA photocatalytic treatment was undertaken to study sulfur evolution. Methods: Photocatalytic runs were performed using a UVA lamp (λmax = 352 nm), open to the air or under N2. A suspension of the corresponding TM or 2-SBA salt and TiO2 was prepared, and pH was adjusted. Suspensions were stirred in the dark for 30 min and then irradiated. TM, 2-MBA, 2-SBA, and C2H5Hg+ were quantified by HPLC, sulfur by TXRF, and the deposits on the photocatalyst were analyzed by chemical reactions. The mineralization degree was followed by TOC. Sulfate was determined using BaCl2 at 580 nm. Results: Photocatalytic destruction of TM and total C2H5Hg+ was complete under N2 and air, but TM degradation was much faster in air. The evolution of TM and the products followed a pseudo-first-order kinetics. Conclusion: TiO2-photocatalytic degradation is a suitable technique for the treatment of TM and its degradation products. In contrast to other organomercurial compounds, TM degradation is faster in the presence of O2, indicating that the oxidative mechanism is the preferred pathway. A significant TM mineralization (> 60%, NPOC and total S) was obtained. TM was more easily degraded than 2-SBA. Sulfate was the final product.

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