A thermodynamic study on the binding of mercury and silver ions to urease

Behbehani, G. Rezaei; Saboury, Ali Akbar; Taherkhani, Ali; Barzegar, L.; Mollaagazade, A.

doi:10.1007/s10973-011-1729-9

Cited by 14 publications

(13 citation statements)

References 12 publications

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“…Previous literature reports that ionic silver is the most effective metal inhibitor of urease and that various other metals such as ionic zinc are also effective albeit to a lesser extent. 2,21,28,37 In the context of synthetic urine, ionic silver was also more effective than ionic zinc as indicted by a lower concentration of silver than zinc being able to maintain constant conductivity and constant pH. However, the results in Fig.…”

Section: Inhibition Of Urea Hydrolysis Through Chemical Additionsmentioning

confidence: 95%

“…The mechanism behind zinc and silver's inhibition of urease can be explained by a number of different functions such as promotion of urease aggregation, induction of protein polymerization, and/or the metal ions binding to the protein's function groups such as thiols (R-SH) and possibly the nitrogen and oxygen centers. 2,20,21 Previous research on metal ion interactions with the urease enzyme revealed that the silver ion can bind with around 50-60% of urease's thiol groups resulting in complete inactivation. 20 Ionic zinc (as zinc nitrate) and ionic silver (as silver nitrate) were chosen due to their strength as urease inhibitors found in the medical and soil science literature.…”

Section: Inhibition Of Urea Hydrolysis Through Chemical Additionsmentioning

confidence: 99%

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Characterization of urea hydrolysis in fresh human urine and inhibition by chemical addition

Ray

Saetta

Boyer

2018

Environ. Sci.: Water Res. Technol.

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Section: Inhibition Of Urea Hydrolysis Through Chemical Additionsmentioning

confidence: 95%

Section: Inhibition Of Urea Hydrolysis Through Chemical Additionsmentioning

confidence: 99%

Characterization of urea hydrolysis in fresh human urine and inhibition by chemical addition

Ray

Saetta

Boyer

2018

Environ. Sci.: Water Res. Technol.

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“…The main classes of urease inhibitors are: boroncontaining compounds [7], thiol compounds [13], phosphate [15], phosphoroamide compounds [17], hydroxamic acids [14], F − ions [18], and heavy metal ions [19,20]. Among the known inhibitors of urease, the inhibition of urease by heavy metal ions is said to result from the reaction of these ions with a sulfhydryl group in the active center of the enzyme by a reaction analogous to the formation of metal sulfides [21].…”

Section: Introductionmentioning

confidence: 99%

Kinetics and mechanism of jack bean urease inhibition by Hg2+

Chen

Liu

et al. 2012

Chemistry Central Journal

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BackgroundJack bean urease (EC 3.5.1.5) is a metalloenzyme, which catalyzes the hydrolysis of urea to produce ammonia and carbon dioxide. The heavy metal ions are common inhibitors to control the rate of the enzymatic urea hydrolysis, which take the Hg2+ as the representative. Hg2+ affects the enzyme activity causing loss of the biological function of the enzyme, which threatens the survival of many microorganism and plants. However, inhibitory kinetics of urease by the low concentration Hg2+ has not been explored fully. In this study, the inhibitory effect of the low concentration Hg2+ on jack bean urease was investigated in order to elucidate the mechanism of Hg2+ inhibition.ResultsAccording to the kinetic parameters for the enzyme obtained from Lineweaver–Burk plot, it is shown that the Km is equal to 4.6±0.3 mM and Vm is equal to 29.8±1.7 μmol NH3/min mg. The results show that the inhibition of jack bean urease by Hg2+ at low concentration is a reversible reaction. Equilibrium constants have been determined for Hg2+ binding with the enzyme or the enzyme-substrate complexes (Ki =0.012 μM). The results show that the Hg2+ is a noncompetitive inhibitor. In addition, the kinetics of enzyme inhibition by the low concentration Hg2+ has been studied using the kinetic method of the substrate reaction. The results suggest that the enzyme first reversibly and quickly binds Hg2+ and then undergoes a slow reversible course to inactivation. Furthermore, the rate constant of the forward reactions (k+0) is much larger than the rate constant of the reverse reactions (k-0). By combining with the fact that the enzyme activity is almost completely lost at high concentration, the enzyme is completely inactivated when the Hg2+ concentration is high enough.ConclusionsThese results suggest that Hg2+ has great impacts on the urease activity and the established inhibition kinetics model is suitable.

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“…This investigation is the first of its kind performed for these systems. Earlier, only prefatory results on the thermodynamics of urease inhibition by heavy metal ions were reported in this journal [68,69]. In this present work, the thermodynamics of the binding of the chosen inhibitors to the enzyme is comprehensively studied, interpreted in terms of their affinity to the enzyme and compared with the binding of the substrate.…”

Section: Competitive Inhibitionmentioning

confidence: 91%

“…and Cd 2? ions, measured with use of isothermal titration calorimetry [68][69][70]. Importantly, unlike the competitive inhibitors in this work, heavy metal ions are comparatively strong inhibitors of urease, strongest being Hg 2?…”

Section: Effect Of Temperature On K Imentioning

confidence: 99%

Thermodynamic study of competitive inhibitors’ binding to urease

Krajewska

Brindell

2015

J Therm Anal Calorim

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Three competitive inhibitors of urease: boric acid, 2-mercaptoethanol and phosphate buffer pH 6.45, were subjected to the studies of temperature effects on their binding to the enzyme. The first of their kind for these systems, the studies were carried out at temperatures between 15 and 35°C in HEPES buffers. The Michaelis K M and inhibition K i constants determined for the uninhibited and inhibited urease reactions, respectively, were found to increase with an increase in temperature, importantly, the inhibition remaining competitive irrespective of temperature. The inverse of the constants were further analyzed as equilibrium constants of substrate and inhibitor binding reactions resulting in the formation of ES and EI complexes. The reactions were thermodynamically analyzed with use of the van't Hoff equation. Found pH-independent in the pH range 6.45-7.0, the changes in the standard enthalpy (DH°= -14 kJ mol -1 ) and the Gibbs free energy (DG 298 = -14 kJ mol -1 ) for the substrate binding were negative, proving favorable for an exothermic and spontaneous reaction. With the standard entropy change DS°close to zero, the reaction is enthalpy driven. The thermodynamic functions of the inhibitor binding by contrast, were found strongly correlated with the inhibitory strengths of the inhibitors in the order: boric acid [ 2-mercaptoethanol [ phosphate buffer pH 6.45. Accordingly, boric acid demonstrated the changes in the thermodynamic functions considerably bigger (DH°= -42 kJ mol -1 , DG 298 = -23 kJ mol -1 ) than the substrate and the other two inhibitors. Those for 2-mercaptoethanol were DH°= -20 kJ mol -1 and DG 298 = -17 kJ mol -1 , while for phosphate buffer pH 6.45, DH°= -17 kJ mol -1 , and DG 298 = -13 kJ mol -1 , and although slightly bigger, they were found practically comparable in value with those of the substrate, features that apparently result from the comparable values of K M and K i s. Remarkably, the inhibitors showed negative values of DS°(to various degrees) proving that their binding to the enzyme, like that of the substrate, is driven by enthalpy.

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A thermodynamic study on the binding of mercury and silver ions to urease

Cited by 14 publications

References 12 publications

Characterization of urea hydrolysis in fresh human urine and inhibition by chemical addition

Characterization of urea hydrolysis in fresh human urine and inhibition by chemical addition

Kinetics and mechanism of jack bean urease inhibition by Hg2+

Thermodynamic study of competitive inhibitors’ binding to urease

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