THE HYDROLYSIS OF THE CONDENSED PHOSPHATES: II (A). THE ROLE OF THE HYDROGEN ION IN THE HYDROLYSIS OF SODIUM PYROPHOSPHATE: II (B). THE DISSOCIATION CONSTANTS OF PYROPHOSPHORIC ACID

1954 ◽  
Vol 32 (2) ◽  
pp. 174-185 ◽  
Author(s):  
J. D. McGilvery ◽  
Joan Pedley Crowther
Keyword(s):  
Dissociation Constants ◽  
Hydrogen Ion ◽  
Ion Concentration ◽  
Rate Equations ◽  
Hydrogen Ion Concentration ◽  
Pyrophosphoric Acid ◽  
Condensed Phosphates ◽  
Anionic Species ◽  
Hydrolysis Of

The general rate equations for the hydrolysis of pyrophosphate anion proposed by Muus have been proved to be inapplicable over the pH range 2.0 to 11.0. A general rate equation is proposed which is based on the assumption that each anionic species of pyrophosphoric acid hydrolyzes at a rate which depends on its concentration, and that the only role of the hydrogen ion concentration is to determine the proportion of each species present in the solution. A mechanism for the hydrolysis of pyrophosphate anion is suggested.The dissociation constants of pyrophosphoric acid have been determined at 65.5 °C. for the concentration range 0.08 to 0.18 molar.

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.

Protein Dissimilation by Human Salivary-sediment Bacteria

1989 ◽  
Vol 68 (2) ◽  
pp. 124-129 ◽  
Author(s):  
E.C. Reynolds ◽  
P.F. Riley
Keyword(s):  
Histone H3 ◽  
Oral Bacteria ◽  
Hydrogen Ion ◽  
Ion Concentration ◽  
Ammonium Ion ◽  
Ph Homeostasis ◽  
Hydrogen Ion Concentration ◽  
Plaque Ph ◽  
Sediment Bacteria ◽  
Hydrolysis Of

Proteins of known composition and structural characteristics were incubated (1.0 mglmL) with re-suspended salivary sediment (2.5% vl v) in a lactate-salt medium with an initial pH of 5.2 for two hr at 37°C. Hydrolysis of the proteins was monitored by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Hydrogen ion, amines, and ammonia were measured by use of a combined pH electrode, high performance liquid chromatography, and glutamate dehydrogenase, respectively. Of the proteins studied, the caseins αs1, β, and K and the histones H1 and H3 were extensively hydrolyzed by the salivary-sediment bacteria. The hydrolysis of these proteins was attributed to their relative lack of tertiary (folded) structure. The only amine detected was the polyamine putrescine arising from the catabolism of arginine following the hydrolysis of the arginine-rich histone H3. None of the other proteins extensively hydrolyzed by salivary sediment, although containing arginyl and lysyl residues, served as substrates for putrescine or cadaverine production. Pre-hydrolysis of the arginine-rich histone H3 and poly-L-arginine with trypsin resulted in a marked increase in putrescine produced, suggesting that the salivary-sediment proteolytic activity was not "trypsin-like". Incubation of salivary-sediment bacteria with the caseins and the histone H3 resulted in an increase in ammonium ion concentration and an associated decrease in hydrogen ion concentration. The increase in ammonium ion concentration not attributed to arginine hydrolysis was correlated with the content of glutaminyl plus asparaginyl residues of the proteins. The results suggest that amido nitrogen, in the form of glutaminyl and asparaginyl residues of salivary and dietary proteins, is a potential source of nitrogen for oral bacteria and may also play a role in plaque pH homeostasis.

scholarly journals THE SIGNIFICANCE OF THE HYDROGEN ION CONCENTRATION FOR THE DIGESTION OF PROTEINS BY PEPSIN

1920 ◽  
Vol 3 (2) ◽  
pp. 211-227 ◽  
Author(s):  
John H. Northrop
Keyword(s):  
Enzyme Preparation ◽  
Proteolytic Enzymes ◽  
Quantitative Agreement ◽  
Hydrogen Ion ◽  
Ion Concentration ◽  
Hydrogen Ion Concentration ◽  
Enzyme Preparations ◽  
Weak Bases ◽  
Strong Acids ◽  
Hydrolysis Of

The experiments described above show that the rate of digestion and the conductivity of protein solutions are very closely parallel. If the isoelectric point of a protein is at a lower hydrogen ion concentration than that of another, the conductivity and also the rate of digestion of the first protein extends further to the alkaline side. The optimum hydrogen ion concentration for the rate of digestion and the degree of ionization (conductivity) of gelatin solutions is the same, and the curves for the ionization and rate of digestion as plotted against the pH are nearly parallel throughout. The addition of a salt with the same anion as the acid to a solution of protein already containing the optimum amount of the acid has the same depressing effect on the digestion as has the addition of the equivalent amount of acid. These facts are in quantitative agreement with the hypothesis that the determining factor in the digestion of proteins by pepsin is the amount of ionized protein present in the solution. It was shown in a previous paper that this would also account for the peculiar relation between the rate of digestion and the concentration of protein. The amount of ionized protein in the solution depends on the amount of salt formed between the protein (a weak base) and the acid. This quantity, in turn, according to the hydrolysis theory of the salts of weak bases and strong acids, is a function of the hydrogen ion concentration, up to the point at which all the protein is combined with the acid as a salt. This point is the optimum hydrogen ion concentration for digestion, since the solution now contains the maximum concentration of protein ions. The hydrogen ion concentration in this range therefore is merely a convenient indicator of the amount of ionized protein present in the solution and takes no active part in the hydrolysis. After sufficient acid has been added to combine with all the protein, i.e. at pH of about 2.0, the further addition of acid serves to depress the ionization of the protein salt by increasing the concentration of the common anion. The hydrogen ion concentration is, therefore, no longer an indicator of the amount of ionized protein present, since this quantity is now determined by the anion concentration. Hence on the acid side of the optimum the addition of the same concentration of anion should have the same influence on the rate of digestion irrespective of whether it is combined with hydrogen or some other ion (provided, of course, that there is no other secondary effect of the other ion). The proposed mechanism is very similar to that suggested by Stieglitz and his coworkers for the hydrolysis of the imido esters. Pekelharing and Ringer have shown that pure pepsin in acid solution is always negatively charged; i.e., it is an anion. The experiments described above show further that it behaves just as would be expected of any anion in the presence of a salt containing the protein ion as the cation and as has been shown by Loeb to be the case with inorganic anions. Nothing has been said in regard to the quantitative agreement between the increasing amounts of ionized protein found in the solution (as shown by the conductivity values) and the amount predicted by the hydrolysis theory of the formation of salts of weak bases and strong acids. There is little doubt that the values are in qualitative agreement with such a theory. In order to make a quantitative comparison, however, it would be necessary to know the ionization constant of the protein and of the protein salt and also the number of hydroxyl (or amino) groups in the protein molecule as well as the molecular weight of the protein. Since these values are not known with any degree of certainty there appears to be no value at present in attempting to apply the hydrolysis equations to the data obtained. It it clear that the hypothesis as outlined above for the hydrolysis of proteins by pepsin cannot be extended directly to enzymes in general, since in many cases the substrate is not known to exist in an ionized condition at all. It is possible, however, that ionization is really present or that the equilibrium instead of being ionic is between two tautomeric forms of the substrate, only one of which is attacked by the enzyme. Furthermore, it is clear that even in the case of proteins there are difficulties in the way since the pepsin obtained from young animals, or a similar enzyme preparation from yeast or other microorganisms, is said to have a different optimum hydrogen ion concentration than that found for the pepsin used in these experiments. The activity of these enzyme preparations therefore would not be found to depend on the ionization of the protein. It is possible of course that the enzyme preparations mentioned may contain several proteolytic enzymes and that the action observed is a combination of the action of several enzymes. Dernby has shown that this is a very probable explanation of the action of the autolytic enzymes. The optimum hydrogen ion concentration for the activity of the pepsin used in these experiments agrees very closely with that found by Ringer for pepsin prepared by him directly from gastric juice and very carefully purified. Ringer's pepsin probably represents as pure an enzyme preparation as it is possible to prepare. There is every reason to suppose therefore that the enzyme used in this work was not a mixture of several enzymes.

The Functional Groups of the Mg–Ca ATPase from Escherichia coli

1975 ◽  
Vol 53 (6) ◽  
pp. 658-665 ◽  
Author(s):  
Jan Ahlers ◽  
Doris Kabisch ◽  
Theodor Günther
Keyword(s):  
Escherichia Coli ◽  
Metal Ion ◽  
Experimental Error ◽  
Dissociation Constants ◽  
Hydrogen Ion ◽  
Ion Concentration ◽  
Hydrogen Ion Concentration ◽  
E Coli ◽  
Membrane Bound ◽  
Arginyl Residues

The influence of hydrogen ion concentration on binding and conversion of MgATP and CaATP by membrane bound and solubilized ATPase from Escherichia coli has been investigated. The reaction of enzyme (E), hydrogen ion (H+), and substrate (S) proceeds according to the following scheme, where Me is the metal ion and P is the product(s).[Formula: see text]Within experimental error, the results obtained with membrane-bound and solubilized ATPase are identical. Changing the concentration of Mg2+ ions or replacement of Mg2+ by Ca2+ ions alters the dissociation constants Kb, KHMeATP, and [Formula: see text]. The kinetics and experiments with group-specific inhibitors suggest that integrity for amino, imidazole, tyrosyl, carboxyl, and arginyl residues is required for activity of membrane-bound and solubilized E. coli ATPase.

scholarly journals Studies in the mechanism of enzyme action. I.—Rôle of the reaction of the medium in fixing the optimum temperature of a ferment

1921 ◽  
Vol 92 (642) ◽  
pp. 1-6 ◽  
Keyword(s):  
Enzyme Activity ◽  
Temperature Effect ◽  
Acid Medium ◽  
Hydrogen Ion ◽  
Ion Concentration ◽  
Optimum Temperature ◽  
Hydrogen Ion Concentration ◽  
Enzyme Action

Previously, it has been shown for the enzyme maltase —enzyme requiring an acid medium in which to act to best advantage—that increase in the acidity or hydrogen ion concentration of the medium in which the enzyme acts, beyond the optimum acidity, leads to a fall of optimum temperature. The mechanism of his temperature of this temperature effect appears clearly to be due to a certain disablement of the enzyme activity, estimated at the optimum temperature point; which decrease of activity is itself a function of the degree of acidity of the medium in excess of that necessary to produce optimum activation. Being in this way a disablement effect, the question arises whether, by adding to the quantity of enzyme in action, the lowering of optimum temperature which takes place can be controlled. To answer that question, the experiments described in the present paper were undertaken. For the investigation, the enzyme used is the maltase of Aspergillus oryzœ , the same preparation being employed as studied by us in two previous communications, a specially active specimen of takadiastase, purified by repeated solution in water and reprecipitation by alcohol.

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