Why is the hydrolytic activity of acetylcholinesterase pH dependent? Kinetic study of acetylcholine and acetylthiocholine hydrolysis catalyzed by acetylcholinesterase from electric eel

2018 ◽  
Vol 73 (9-10) ◽  
pp. 345-351 ◽  
Author(s):  
Alena Komersová ◽  
Markéta Kovářová ◽  
Karel Komers ◽  
Václav Lochař ◽  
Alexander Čegan
Keyword(s):  
Catalytic Activity ◽  
Ionic Strength ◽  
Ph Value ◽  
Hydrolytic Activity ◽  
Initial Substrate ◽  
Electric Eel ◽  
Value Range ◽  
Ph Dependent ◽  
Ph Range ◽  
Initial Substrate Concentration

AbstractThe dependence of the activity of acetylcholinesterase from electric eel at a pH value range of 4.8–9.8 (phosphate buffer), regarding acetylcholine and acetylthiocholine hydrolysis, was determined at 25 °C, ionic strength of 0.11 M, and initial substrate concentration of 4 mM. At a pH range of 4.8–9.8, the dependencesA(pH) form a sigmoid increasing curve with the maximum catalytic activity at a pH range 8–9.5. For acetylcholine hydrolysis, the kinetic reason for such an increase inAconsists mainly of an increase in the rate constantk2(Michaelis-Menten) model with increasing pH of the reaction mixture. For acetylthiocholine hydrolysis, the kinetic explication of the determined dependenceA(pH) is more complicated.

scholarly journals Zinc adsorption in highly weathered soils

2008 ◽  
Vol 43 (1) ◽  
pp. 131-139 ◽  
Author(s):  
José Carlos Casagrande ◽  
Marcio Roberto Soares ◽  
Ernesto Rinaldi Mouta
Keyword(s):  
Ionic Strength ◽  
Ph Value ◽  
Batch Adsorption ◽  
Adsorption Mechanisms ◽  
Ionic Strength Effect ◽  
Ph Values ◽  
Effects Of Ph ◽  
Ph Range ◽  
Highly Weathered Soils ◽  
Zinc Adsorption

The objective of this work was to assess the effects of pH and ionic strength upon zinc adsorption, in three highly weathered variable charge soils. Adsorption isotherms were elaborated from batch adsorption experiments, with increasing Zn concentrations (0-80 mg L-1), and adsorption envelopes were constructed through soil samples reactions with 0.01, 0.1 and 1 mol L-1 Ca(NO3)2 solutions containing 5 mg L-1 of Zn, with an increasing pH value from 3 to 8. Driving force of reaction was quantified by Gibbs free energy and separation factor. Isotherms were C-, H- and L-type and experimental results were fitted to nonlinear Langmuir model. Maximum adsorption ranged from 59-810 mg kg-1, and Zn affinity was greater in subsoil (0.13-0.81 L kg-1) than in the topsoil samples (0.01-0.34 L kg-1). Zinc adsorption was favorable and spontaneous, and showed sharply increase (20-90%) in the 4-6 pH range. No effect of ionic strength was observed at pH values below 5, because specific adsorption mechanisms predominated in the 3-5 pH range. Above pH 5, and in subsoil samples, Zn was adsorbed by electrostatic mechanisms, since ionic strength effect was observed. Despite depth and ionic strength effects, Zn adsorption depends mainly on the pH.

The Coagulability of Partially Lysed Fibrinogen Effect of pH and Ionic Strength

1971 ◽  
Vol 25 (02) ◽  
pp. 346-353 ◽  
Author(s):  
D. C Triantaphyllopoulos ◽  
Mary Torres
Keyword(s):  
Ionic Strength ◽  
Human Plasma ◽  
Ammonium Sulfate ◽  
Inverse Relationship ◽  
Ph Value ◽  
Distilled Water ◽  
Human Fibrinogen ◽  
Ph Values ◽  
Ph Dependent ◽  
Limited Digestion

SummaryAddition of thrombin to plasma obtained from dogs injected with plasmin clotted more fibrinogen when the plasma was diluted with saline than when it was diluted with distilled water. In contrast, more fibrin was formed in dilutions with distilled water when thrombin was added to intact plasma obtained prior to the injection of plasmin.The same phenomenon was observed with purified human fibrinogen submitted to limited digestion with plasmin and was found to be pH dependent. When the pH was greater than 7.3 more fibrin was formed if the fibrinogen was diluted with saline than if it was diluted with distilled water. The opposite was observed at pH values lower than 7.2.Similar results were obtained with the fraction of partially lysed human fibrinogen which precipitates at 25% saturation with ammonium sulfate. The same fraction, however, obtained from partially digested bovine fibrinogen did not react exactly the same way. In dilutions with distilled water there was an inverse relationship between the pH value and the amount of protein which clotted; but the reverse did not apply to the same extent in dilutions with saline.At variance to the above observations the clottability of purified intact fibrinogen was not significantly altered by changes in pH or in ionic strength.The clottability of partially lysed human plasma could be reversed (more fibrin in distilled water than in saline) after exhaustive dialysis against oxalated (pH 7.0) but not against citrated (pH 7.8) saline indicating that the change in clottability was due to a change in pH.

scholarly journals Metal Ions and Hydrogen Peroxide. XXV

1972 ◽  
Vol 27 (2) ◽  
pp. 95-100 ◽  
Author(s):  
Peter Waldmeier ◽  
Bernhard Prijs ◽  
Helmut Sigel
Keyword(s):  
Hydrogen Peroxide ◽  
Ionic Strength ◽  
Metal Ions ◽  
Experimental Evidence ◽  
Initial Rate ◽  
Reaction Order ◽  
Ph Dependence ◽  
Initial Concentration ◽  
Ph Dependent ◽  
Ph Range

The decomposition of H2O2, catalyzed by the Co2® complex of 4,4′,4″,4″′-tetrasulfophthalocyanine (CoIIPTS), was investigated in the pH range 3.8 through 10 by measuring the initial rate, v0=d(O2)/dt, of the increasing formation of O2 (25°; I=0.1). In this pH range v0 is proportional to the initial concentration of H2O2 (determined at pH 5.0 and 9.2). Due to the dimerization (log KD=5.47 ±0.09 at natural ionic strength and about 7.63 ±0.16 in 0.1 M NaClO4; 25°) and polymerization of CoIIPTS the catalyst and its reaction order are difficult to establish: Based on the experimental evidence it is suggested that v0 is proportional to the concentration of monomer CoIIPTS. Additionally, there is evidence that the experimentally determined v0 contains the contributions of a pH-independent and a pH-dependent reaction course. These results are analog to those obtained earlier with FeIIIPTS as catalyst. A mechanism for the catalyzed disproportionation of H2O2 by CoIIPTS is proposed. The catalase-like activity of CoIIIPTS (OH) is smaller than that of CoIIPTS and the pH-dependence is different.

scholarly journals The pathway of myo-inositol 1,3,4-trisphosphate dephosphorylation in liver

1987 ◽  
Vol 248 (3) ◽  
pp. 977-980 ◽  
Author(s):  
S B Shears ◽  
C J Kirk ◽  
R H Michell
Keyword(s):  
Enzyme Activity ◽  
Ionic Strength ◽  
Substrate Concentration ◽  
Initial Substrate ◽  
Liver Homogenates ◽  
Initial Substrate Concentration

We studied the dephosphorylation pathway for Ins(1,3,4)P3 (inositol 1,3,4-trisphosphate) by liver homogenates and soluble and particulate subfractions incubated in media resembling physiological ionic strength and pH. Ins(1,3,4)P3 was dephosphorylated to two InsP2 (inositol bisphosphate) isomers, one of which is Ins(3,4)P2 [Shears, Parry, Tang, Irvine, Michell & Kirk (1987) Biochem. J. 246, 139-147]. The second InsP2 is the 1,3 isomer. Ins(3,4)P2 is dephosphorylated to inositol 3-phosphate by an enzyme activity located in both soluble and particulate fractions. The phosphatase(s) that attacks Ins(1,3)P2 was largely soluble, but we have not determined which phosphate(s) is removed. When the initial substrate concentration was 1 nM, the rate of dephosphorylation of Ins(1,4)P2 greater than Ins(1,3)P2 greater than Ins(3,4)P2. None of these bisphosphates was phosphorylated when incubated with liver homogenates and 5 mM-ATP, but their rates of dephosphorylation were then decreased.

scholarly journals Local pH-dependent conformational changes leading to proteolytic susceptibility of cystatin C

1994 ◽  
Vol 302 (2) ◽  
pp. 411-416 ◽  
Author(s):  
P J Berti ◽  
A C Storer
Keyword(s):  
Ionic Strength ◽  
Conformational Change ◽  
Cystatin C ◽  
Conformational Changes ◽  
Ph Dependence ◽  
Significant Proportion ◽  
Cysteine Protease Inhibitor ◽  
Ionic Strength Dependence ◽  
Ph Dependent ◽  
Ph Range

Cystatin C, a cysteine protease inhibitor, was subject to hydrolysis at two sites when complexed with papain and in the presence of excess papain. A pH-dependent cleavage at His-86 increases Asp-87 was observed, as well as a pH-independent one at Gly-4 increases Lys-5. His-86 increases Asp-87 hydrolysis increased with decreasing pH and was characterized kinetically. It could be described by a single ionization with pKa = 3.4 +/- 0.2 and (kcat./Km)max. = 1.4 (+/- 0.4) x 10(4) M-1.s-1 at I = 0.3 M. C.d. spectroscopy, also at I = 0.3 M, demonstrated a conformational change with pKa = 3.2 +/- 0.2, indicating that the pH-dependence of hydrolysis was due to a conformational change in cystatin C. At I = 0.15 M, the pKa of the conformational change observed by c.d. shifted to 4.1 +/- 0.1. This indicates that at physiological ionic strength of 0.15 M, a significant proportion of cystatin C complexed with protease would be in a proteolytically labile conformation over the pH range 4.5 to 5, which is encountered in lysosomes. This may constitute a mechanism for clearing inappropriately localized cystatins. A pH-dependent conformational variability in this region of the inhibitor could explain the differences in the X-ray crystallographic and n.m.r. structures of the homologous chicken cystatin. The ionic-strength dependence of ionization indicates a hydrophobic stabilization of the ionizable group. The lack of pH-dependence of hydrolysis at Gly-4 increases Lys-5, with kcat./Km = 220 +/- 41 M-1.s-1 in the pH range 3.89 to 7.96 was unexpected in light of the normal, bell-shaped pH-dependence of papain-catalysed hydrolyses. This may reflect a different rate-limiting step of cystatin C hydrolysis.

Aggregation properties of electric eel acetylcholinesterase: a possible mechanism of enzyme association at the synapse

1978 ◽  
Vol 36 (2) ◽  
pp. 186-187
Author(s):  
J. Cartaud ◽  
S. Bon ◽  
J. Massoulié
Keyword(s):  
Catalytic Activity ◽  
Ionic Strength ◽  
Acetylcholinesterase Activity ◽  
Molecular Forms ◽  
Catalytic Subunits ◽  
Electric Eel ◽  
Low Ionic Strength

Electrophorus acetylcholinesterase activity (E.C.3.1.1.7) is associated with several molecular forms (D = 18.5 S, M.W.= 1,150,000; C = 14.4 S, M.W.= 796,000; A = 9 S, M.W. = 410,000; G = 11.8 S, M.W.= 330,000; G' = 7.7 S, M.W.= 165,000 and G” = 5.3 S, M.W. = 70,000). All the lighter forms probably derive from the heaviest (D) which is an asymmetric assembly of three tetramers of catalytic subunits linked by a collagen-like filament or “tail”. The two lighter asymmetric forms, A and C, contain respectively one and two tetramers linked to a tail.When exposed to low ionic strength conditions, the asymmetric forms of the enzyme associate reversibly into fast sedimenting aggregates (70 S), the process not being correlated with any change in catalytic activity.

Influence of Ionic Strength and pH-value on the Silicon Dioxide Polishing Behaviour of Slurries Based on Pure Silica Suspensions

2010 ◽  
Vol 1249 ◽  
Author(s):  
Ulrich Kuenzelmann ◽  
Kathrin Estel ◽  
Johann W Bartha ◽  
Erwin-Peter Meyer ◽  
Herbert Barthel
Keyword(s):  
Ionic Strength ◽  
Fumed Silica ◽  
Ph Value ◽  
Acidic Ph ◽  
Experimental Conditions ◽  
Ph Values ◽  
Pure Silica ◽  
Silica Sols ◽  
Ph Range ◽  
Silica Suspensions

AbstractIn this study, the effect of the addition of electrolytes in a given ionic strength to various high-purity silica suspensions was investigated by measurement of the removal rates (RR's) in CMP processes on oxide layers under the same experimental conditions. As so-called slurries the following suspensions were used: i) silica sols produced by the Stöber process, ii) conventional silica sols based on alkali silicate as well as iii) suspensions of fumed silica, with the same SiO2 concentration in each suspension. Ionic strength of the added electrolyte was adjusted to e.g. 0.065 mol/l, with the electrolytes being HCl, NH4Cl, KOH, or binary mixtures of these substances.These investigations revealed significant differences of the polishing behaviour between the different types of silica dispersions as slurries. While for the Stöber sols investigated, the RR's are highest in the acidic range and almost negligible in the alkaline pH range, fumed silica suspensions show an entirely different behaviour: RR is very low for acidic pH-values, and increases with the alkalinity of the slurry. In contrast to these observations, the RR's of slurries based on conventional silica sols are highest around the neutral point, and show a decrease for both more alkaline and acidic pH-values. In comparison to the other two types of material, these suspensions have a high amount of electrolyte background, originating from their manufacturing process.A model is developed to explain these results in a comprehensive manner. It involves effects of the electrolyte type and the ionic strengths as well as influences of the particle size.

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.

Donnan Equilibria in Polymeric Micellar Systems with Weak Polyelectrolyte Shells: The Lowering of the pH Value

1997 ◽  
Vol 62 (11) ◽  
pp. 1730-1736 ◽  
Author(s):  
Petr Munk ◽  
Zdeněk Tuzar ◽  
Karel Procházka
Keyword(s):  
Ionic Strength ◽  
Block Copolymer ◽  
Ph Value ◽  
Electrolyte Solutions ◽  
Hydrogen Ions ◽  
Micellar Systems ◽  
Weak Electrolytes ◽  
Block Copolymer Micelles ◽  
Copolymer Micelles ◽  
Polyelectrolyte Solutions

When two electrolyte solutions are separated and only some of the ions can cross the boundary, the concentrations of these ions are different on both sides of the boundary. This is the well-known Donnan effect. When weak electrolytes are involved, the imbalance includes also hydrogen ions: there is a difference of pH across the boundary and the dissociation of nondiffusible weak electrolytes is suppressed. The effect is very pronounced when the concentration of the weak electrolyte is high and ionic strength is low. The significance of this phenomenon is discussed for polyelectrolyte solutions, and particularly for block copolymer micelles with weak polyelectrolyte shells. The effect is quite dramatic in the latter case.

scholarly journals The pH-dependent subunit dissociation and catalytic activity of bovine dopamine beta-hydroxylase.

1985 ◽  
Vol 260 (6) ◽  
pp. 3386-3392
Author(s):  
A Saxena ◽  
P Hensley ◽  
J C Osborne ◽  
P J Fleming
Keyword(s):  
Catalytic Activity ◽  
Subunit Dissociation ◽  
Dopamine Beta Hydroxylase ◽  
Ph Dependent
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