ÉTUDE DES EFFETS ÉLECTROSTATIQUES SUR LE MÉCANISME D'ACTION CATALYTIQUE DE LA PHOSPHATASE ALCALINE INTESTINALE DE VEAU

1965 ◽  
Vol 43 (8) ◽  
pp. 2222-2235 ◽  
Author(s):  
Michel Lazdunski ◽  
Jacques Brouillard ◽  
Ludovic Ouellet
Keyword(s):  
Dielectric Constant ◽  
Ionic Strength ◽  
Maximum Activity ◽  
Enzyme Molecule ◽  
High Substrate Concentration ◽  
Nitrophenyl Phosphate ◽  
Phosphatase Alcaline ◽  
Rate Of Hydrolysis ◽  
Hydrolysis Of ◽  
Activated Complex

The influence of dioxane and ethanol on the rate of hydrolysis of p-nitrophenyl phosphate in the presence of an intestinal alcaline phosphatase can be interpreted as a dielectric constant effect, at high substrate concentration. The dielectric constant effect is a function of the pH of the medium and is maximum around pH 9.4 at 25 °C and pH 9.0 at 15 °C. An interpretation suggesting that the change in diameter of the enzyme molecule becoming an activated complex is minimum at a pH of maximum activity is proposed. The same model can take into account the influence of the ionic strength on the same reaction.

PHOSPHATASE ALCALINE INTESTINALE: CINÉTIQUE DE L'HYDROLYSE DU PHOSPHATE DE p-NITROPHÉNYLE

1961 ◽  
Vol 39 (6) ◽  
pp. 1298-1308 ◽  
Author(s):  
Michel Lazdunski ◽  
Ludovic Ouellet
Keyword(s):  
Active Center ◽  
Electrostatic Interactions ◽  
Enzyme Molecule ◽  
Kcal Mole ◽  
Intestinal Alkaline Phosphatase ◽  
High Substrate Concentration ◽  
System P ◽  
Nitrophenyl Phosphate ◽  
Phosphatase Alcaline ◽  
Michaelis Constants

The Michaelis constants and the rates at high substrate concentration for the system p-nitrophenyl phosphate – intestinal alkaline phosphatase have been measured at 15.3 °C and 24.4 °C from pH 7.5 to pH 10.4.The experimental data can be interpreted as indicating the presence of three acid groups in the active center of the enzyme. The observed pK of ionization of these groups are 9.02, 8.39, and 7.65 at 15.3 °C, and 9.75, 8.42, and 7.62 at 24.4 °C.These data stress the importance of electrostatic interactions between the groups in the active center and the rest of the enzyme molecule. A heat of ionization of 6 to 7 kcal/mole is attributed to each of these groups. At least one active group of the enzyme would be a thiol function and the other ones imidazole or thiol.

Kinetics of hydrolysis of peroxodisulphate ions in acidic medium to peroxomonosulphuric acid

1981 ◽  
Vol 46 (5) ◽  
pp. 1229-1236 ◽  
Author(s):  
Jan Balej ◽  
Milada Thumová
Keyword(s):  
Ionic Strength ◽  
Rate Constants ◽  
Acidic Medium ◽  
Measured Data ◽  
Molar Ratios ◽  
Starting Solution ◽  
Kinetics Of Hydrolysis ◽  
Rate Of Hydrolysis ◽  
Kinetics Of ◽  
Hydrolysis Of

The rate of hydrolysis of S2O82- ions in acidic medium to peroxomonosulphuric acid was measured at 20 and 30 °C. The composition of the starting solution corresponded to the anolyte flowing out from an electrolyser for production of this acid or its ammonium salt at various degrees of conversion and starting molar ratios of sulphuric acid to ammonium sulphate. The measured data served to calculate the rate constants at both temperatures on the basis of the earlier proposed mechanism of the hydrolysis, and their dependence on the ionic strength was studied.

scholarly journals Phosphatase synthesis in Klebsiella (Aerobacter) aerogenes growing in continuous culture

1972 ◽  
Vol 127 (1) ◽  
pp. 87-96 ◽  
Author(s):  
P. G. Bolton ◽  
A. C. R. Dean
Keyword(s):  
Alkaline Phosphatase ◽  
Acid Phosphatase ◽  
Continuous Culture ◽  
Activity Profile ◽  
Glucose Effect ◽  
Ph Values ◽  
Nitrophenyl Phosphate ◽  
Wide Range ◽  
Rate Of Hydrolysis ◽  
Hydrolysis Of

1. Phosphatase synthesis was studied in Klebsiella aerogenes grown in a wide range of continuous-culture systems. 2. Maximum acid phosphatase synthesis was associated with nutrient-limited, particularly carbohydrate-limited, growth at a relatively low rate, glucose-limited cells exhibiting the highest activity. Compared with glucose as the carbon-limiting growth material, other sugars not only altered the activity but also changed the pH–activity profile of the enzyme(s). 3. The affinity of the acid phosphatase in glucose-limited cells towards p-nitrophenyl phosphate (Km 0.25–0.43mm) was similar to that of staphylococcal acid phosphatase but was ten times greater than that of the Escherichia coli enzyme. 4. PO43−-limitation derepressed alkaline phosphatase synthesis but the amounts of activity were largely independent of the carbon source used for growth. 5. The enzymes were further differentiated by the effect of adding inhibitors (F−, PO43−) and sugars to the reaction mixture during the assays. In particular, it was shown that adding glucose, but not other sugars, stimulated the rate of hydrolysis of p-nitrophenyl phosphate by the acid phosphatase in carbohydrate-limited cells at low pH values (<4.6) but inhibited it at high pH values (>4.6). Alkaline phosphatase activity was unaffected. 6. The function of phosphatases in general is discussed and possible mechanisms for the glucose effect are outlined.

Etude cinétique des interactions électrostatiques entre la phosphatase alcaline intestinale de veau et ses substrats

1974 ◽  
Vol 52 (17) ◽  
pp. 3087-3097 ◽  
Author(s):  
Marius Julien ◽  
Ludovic Ouellet
Keyword(s):  
Dielectric Constants ◽  
Enzyme Molecule ◽  
Ionic Charge ◽  
Substrate Molecule ◽  
Net Charge ◽  
Organic Part ◽  
Enzyme Substrate ◽  
Nitrophenyl Phosphate ◽  
Phosphatase Alcaline ◽  
Ethanolamine Phosphate

The role played by the ionic charge of the enzyme in the kinetics of the reactions catalyzed by alkaline phosphatases has been investigated. Data obtained from the hydrolysis of p-nitrophenyl phosphate (net charge −2) indicate that the repulsion between the negatively charged enzyme molecule and the substrate molecule is sufficient to take into account, quantitatively, the variation of the Michaelis constant with the pH of the system between pH 8.5 and 10.5. However, the results obtained with ethanolamine phosphate (net charge −1) and p- or o-carboxyphenyl phosphate (net charge −3) show that either the organic part of the substrate molecule is not involved in the formation of the enzyme substrate intermediate or the charge of the enzyme does not have the role suggested from the work with p-nitrophenyl phosphate.Further investigation of this reaction in solutions of various ionic strength and dielectric constants suggests that the active center of the enzyme molecule is positively charged, but that hydrophobic effects are important.

Mechanistic Information from the Effect of Pressure on the Kinetics of Hydrolysis of Iodopentaaquochromium(III) Ion

1975 ◽  
Vol 53 (24) ◽  
pp. 3697-3701 ◽  
Author(s):  
Milton Cornelius Weekes ◽  
Thomas Wilson Swaddle
Keyword(s):  
Ionic Strength ◽  
Hydrogen Ion ◽  
Ion Concentration ◽  
Hydrogen Ion Concentration ◽  
Kinetics Of Hydrolysis ◽  
Rate Of Hydrolysis ◽  
Kinetics Of ◽  
Hydrolysis Of ◽  
Aqueous Hclo ◽  
Conjugate Base

The rate of hydrolysis of iodopentaaquochromium(III) ion has been measured as a function of pressure (0.1 to 250 MPa) and hydrogen ion concentration (0.1 to 1.0 mol kg−1) at 298.2 K and ionic strength 1.0 mol kg−1 (aqueous HClO4–LiClO4). The volumes of activation for the acid independent and inversely acid dependent hydrolysis pathways are −5.4 ± 0.5 and −1.6 ± 0.3 cm3 mol−1 respectively, and are not detectably pressure-dependent. Consideration of these values, together with the molar volume change of −3.3 ± 0.3 cm3 mol−1 determined dilatometrically for the completed hydrolysis reaction, indicates that the mechanisms of the two pathways are associative interchange (Ia) and dissociative conjugate base (Dcb) respectively.

Some Characteristics of the Enzymes of the Pyloric Caeca of Cod and Haddock

1937 ◽  
Vol 3 (5) ◽  
pp. 473-485 ◽  
Author(s):  
W. W. Johnston
Keyword(s):  
Protease Activity ◽  
Room Temperature ◽  
Maximum Activity ◽  
Hydrogen Ion ◽  
Ammonium Salts ◽  
Ion Concentrations ◽  
Pyloric Caeca ◽  
Rate Of Hydrolysis ◽  
Hydrolysis Of ◽  
Partial Vacuum

Investigation of fish enzymes for leather bates reveals that those of the pyloric caeca show their greatest influence on casein and collagen at hydrogen ion concentrations of approximately pH 8. The protease showed its maximum activity towards casein at a temperature of 45 °C. Ammonium salts at certain concentrations increased the rate of hydrolysis of collagen by about 40 per cent, but had no like stimulating effect on the hydrolysis of casein. A comparison showed that pyloric caeca enzymes were just as satisfactory as commercial leather bates or hog pancreas. When the pyloric caeca are allowed to autolyse at room temperature, the protease activity is constant for the first 24 hours, declines rapidly during the next 80 hours, and slowly thereafter. The most suitable method for preparing a dried preparation was by evaporation under partial vacuum, which, however, is accompanied by some loss of activity.

scholarly journals Properties of methyl acetimidate and its use as a protein-modifying reagent

1981 ◽  
Vol 193 (1) ◽  
pp. 245-249 ◽  
Author(s):  
A J Makoff ◽  
A D B Malcolm
Keyword(s):  
Ionic Strength ◽  
Rate Constants ◽  
Reaction Mechanisms ◽  
Effect Of Ph ◽  
Rate Of Hydrolysis ◽  
Hydrolysis Of

The rate of hydrolysis of the imido ester methyl acetimidate and its rate of amidination of denatured aldolase were investigated under different conditions of temperature, pH and ionic strength. Both rate constants increase greatly with temperature, whereas ionic strength has no effect on either. The effect of pH is more complex. Between pH 6.8 and 8.8 the rate of hydrolysis decreases and the rate of amidination increases. These results are discussed in terms of the reaction mechanisms involved.

scholarly journals Effect of the Medium Dielectric Strength on the Activity of Alpha Chymotrypsin

1959 ◽  
Vol 43 (1) ◽  
pp. 127-137 ◽  
Author(s):  
M. Castañeda-Agulló ◽  
Luz M. del Castillo
Keyword(s):  
Dielectric Constant ◽  
Dielectric Strength ◽  
Negative Ion ◽  
Enzymatic Reactions ◽  
Specific Effects ◽  
Low Concentrations ◽  
Dielectric Effect ◽  
Rate Of Hydrolysis ◽  
Hydrolysis Of ◽  
Positive Ion

The rates of hydrolysis of TrEE, TEE, and ATEE1 by α-chymotrypsin were determined in media of variable dielectric strength. Many substances which modify the dielectric constant of the medium, exert additional specific effects on the reaction rate, noticeable at more or less elevated concentrations. Notwithstanding, it is possible to differentiate the dielectric and specific effects by comparing the rates in solvents of distinct nature at relatively low concentrations. Thus, the effect of varying the dielectric strength could be studied within wider ranges (ΔD = 20 with TrEE and ca. 28 with ATEE) than in the previous study of trypsin (ΔD = 12). The dielectric effect on α-chymotrypsin is the opposite of that observed with trypsin. In both cases there is a linear relationship between the logarithm of the rate of hydrolysis and the reciprocal of the dielectric constant. The slope is negative with α-chymotrypsin and positive with trypsin. According to expressions relating the dielectric constant to the rate in non-enzymatic reactions, the behavior of α-chymotrypsin is like that of a negative ion, while trypsin behaves as a positive ion. The enzyme activity appears to depend upon the arrangement of charges in the enzyme and substrate molecules, rather than on the presence of certain atomic groupings in the substrate.

Kinetics of Acid-Catalysed Hydrolysis of Diethylsuccinate in Dioxane-Water Mixtures

1982 ◽  
Vol 37 (4) ◽  
pp. 390-394
Author(s):  
Fayez Y . Khalil ◽  
F. M. Abdel-Halim ◽  
Adel N. Asaad
Keyword(s):  
Dielectric Constant ◽  
Thermodynamic Parameters ◽  
Rate Constants ◽  
Solvent Composition ◽  
Specific Rate ◽  
Molecular Dipole ◽  
First Order ◽  
Kinetics Of ◽  
Hydrolysis Of ◽  
Activated Complex

Abstract The specific rate constants k1 and k2 of the consecutive first-order acid-catalysed hydrolysis steps of diethylsuccinate in dioxane-water mixtures covering the range 0-95% (w/w) of dioxane are determined at 25-55 °C. As the concentration of dioxane increases, the rate of the reaction decreases to a minimum at about 90% (w/w) dioxane, after which it increases again. The ratio k1/k2 was found to be almost constant at the value 2.0. The activation energies of the reaction are independent of solvent composition. Available electrostatic theories regarding the effect of the dielectric constant on the rate are presented, from which the reaction is shown to be an ion-molecular dipole type of interaction. The thermodynamic parameters and the radii of the activated complex at different solvent compositions are calculated and discussed.

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