scholarly journals The binding of ethyl isocyanide to ferroperoxidase

1972 ◽  
Vol 128 (2) ◽  
pp. 377-382 ◽  
Author(s):  
Charles Phelps ◽  
Eraldo Antonini ◽  
Maurizio Brunori
Keyword(s):  
Process Model ◽  
Dissociation Constants ◽  
Ph Dependence ◽  
Affinity Constant ◽  
Dependent Manner ◽  
Ph Values ◽  
Cyanide Binding ◽  
Equilibrium And Kinetics ◽  
Kinetics Of ◽  
A New Species

The equilibrium and kinetics of ethyl isocyanide binding to ferroperoxidase were studied. At pH9.1 the results of both studies are consistent with a single-process model with an affinity constant of 95m−1 and combination and dissociation constants of 2.2×103m−1·s−1 and 23s−1 respectively. Ethyl isocyanide is not bound significantly at pH values lower than 6.0, and in this behaviour and the pH-dependence of the affinity constant, similarities exist between isocyanide and cyanide binding. The enthalpy of the process measured by equilibrium methods is −59kJ/mol (−14kcal/mol). At pH values below 9, the ethyl isocyanide adduct changes in a slow time-dependent manner, giving rise to a new species. These changes are reversible on increasing the pH. The results are discussed in relation to other known information about ligand binding to ferroperoxidase and to myoglobin.

scholarly journals The binding of cyanide to ferroperoxidase

1971 ◽  
Vol 122 (1) ◽  
pp. 79-87 ◽  
Author(s):  
Charles Phelps ◽  
Eraldo Antonini ◽  
Maurizio Brunori
Keyword(s):  
Sodium Dithionite ◽  
Affinity Constant ◽  
Kinetic Measurements ◽  
First Order ◽  
Ph Values ◽  
Cyanide Binding ◽  
Single Process ◽  
Ph Jump ◽  
Equilibrium And Kinetics ◽  
Kinetics Of

1. The equilibrium and kinetics of cyanide binding to ferroperoxidase were investigated. At pH9.1 the equilibrium and kinetic measurements agree closely and disclose a single process with an affinity constant of 1.1×103m@!-1 and combination and dissociation velocity constants of 29m-1·s-1 and 2.5×10-2s-1 respectively. 2. At pH values below 8 the affinity constant falls until at pH6.0 the ferroperoxidase·cyanide complex is no longer formed. This is shown to be associated with the formation of ferriperoxidase·cyanide complex in the mixture even in the presence of excess of sodium dithionite. 3. Rapid-pH-jump experiments show a fast pseudo-first-order interconversion between ferroperoxidase·cyanide complex at pH9.1 and ferriperoxidase·cyanide complex at pH6.0. 4. The kinetics of binding of cyanide to dithionite-reduced peroxidase at pH6.0 are complicated and radically different from those observed at pH9.1. 5. Above pH8 the change of affinity constant with pH is consistent with the undissociated species, HCN, being bound by the ferroperoxidase. The enthalpy for this process measured both by equilibrium and kinetic methods is about -8kcal/mol. 6. The binding of cyanide to reconstituted peroxidases, proto, meso and deutero, was investigated. 7. The results are discussed in relation to known data on cyanide binding to other haemoproteins.

Equilibrium and Kinetics of the Extraction of Gallium(III) from Sodium Hydroxide Solutions with 7-Dodecenyl-8-quinolinol (Kelex 100)

1993 ◽  
Vol 58 (5) ◽  
pp. 1093-1102 ◽  
Author(s):  
Aleksandra A. Mitrovic ◽  
Slobodan K. Milonjic ◽  
Zoja E. Ilic ◽  
Radomir V. Stevanovic
Keyword(s):  
Sodium Hydroxide ◽  
Sodium Hydroxide Solution ◽  
Aqueous Sodium Hydroxide ◽  
Sodium Concentration ◽  
Extraction Kinetics ◽  
Aqueous Sodium Hydroxide Solution ◽  
Ph Values ◽  
Constant Ph ◽  
Equilibrium And Kinetics ◽  
Kinetics Of

The influence of hydroxide ions concentration of the aqueous sodium hydroxide solution, at constant sodium concentrations, on the gallium extraction with Kelex 100 was examined in the hydroxide concentration range from 0.02 to 0.5 mol dm-3. The percentage of extracted gallium increases from 51% to 98% within the investigated hydroxide concentration range. The influence of sodium concentrations (from 1 to 6 mol dm-3) on the gallium extraction was also studied at constant pH values. The decrease of extracted gallium is slight for the sodium concentration up to 3 mol dm-3, while for the higher ones it is pronounced. The extraction kinetics was studied using a mixer-type apparatus. The rate expression of the extraction reaction of gallium with Kellex 100, for both lower and higher hydroxide concentrations are ascertained.

DISSOCIATION AND SUBUNIT SIZE OF β-LIPOVITELLIN

1965 ◽  
Vol 43 (6) ◽  
pp. 661-670 ◽  
Author(s):  
W. H. Cook ◽  
R. A. Wallace
Keyword(s):  
Molecular Weight ◽  
Light Scattering ◽  
Dissociation Constants ◽  
Dry Weight ◽  
Ph Values ◽  
Scattering Measurements ◽  
Solvent Displacement ◽  
Weight Method ◽  
Kinetics Of ◽  
Good Agreement

Dissociation of β-lipovitellin was detectable at pH 5.8 and increased linearly with pH. Light-scattering measurements at different pH values were consistent with a molecular weight of 2.27 × 105 for the subunit and twice this value for the associated form, confirming that it is a monomer–dimer system. This value for the molecular weight of the dimer is somewhat higher than previously reported (4.0 × 105) partly because a solvent displacement correction was used in estimating concentration by a dry weight method. Dissociation constants evaluated from light-scattering measurements and by ultracentrifugal separation were 22 × 10−6 and 29 × 10−6 respectively, in good agreement with provisional values already reported. Preliminary studies on the kinetics of this reaction indicate that, when the pH is altered, dissociation reaches the new equilibrium in about 0.5 minute but that reassociation requires about 50 minutes.

Flow kinetics of immobilized β-glucosidase

1986 ◽  
Vol 64 (2) ◽  
pp. 139-145 ◽  
Author(s):  
Yuchiong Hsuanyu ◽  
Keith J. Laidler
Keyword(s):  
Ph Dependence ◽  
Kinetic Studies ◽  
Free Enzyme ◽  
Diffusion Control ◽  
Michaelis Constant ◽  
Ph Optimum ◽  
Ph Values ◽  
Nylon Tubing ◽  
Kinetics Of ◽  
Substrate Concentrations

The enzyme β-glucosidase was attached covalently to the inner surface of nylon tubing. Flow kinetic studies were carried out at a range of temperatures, pH values, flow rates, and substrate concentrations. Various tests showed that the extent of diffusion control was negligible. At 25 °C the Michaelis constant was 33.4 mM, not greatly different from the value for the enzyme in free solution. The pH dependence was similar to that for the free enzyme. The Arrhenius plots showed inflexions at about 22 °C, as with the free enzyme, the changes in slope being small at the pH optimum of about 5.9 and becoming much more pronounced as the pH is increased or decreased. The immobilized enzyme is more stable than the free enzyme, both on storage at low and higher temperatures, and its reuse stability is greater.

scholarly journals In vitro pH dependent passive transport of ketoprofen and metformin

ADMET & DMPK ◽  
2020 ◽  
Vol 9 (1) ◽  
pp. 57-68
Author(s):  
Alisa Elezović ◽  
Amina Marić ◽  
Amila Biščević ◽  
Jasmina Hadžiabdić ◽  
Selma Škrbo ◽  
...  
Keyword(s):  
Dissociation Constants ◽  
Ph Value ◽  
Passive Transport ◽  
Artificial Membrane ◽  
Ph Values ◽  
A Value ◽  
Model Substances ◽  
Experimental Values ◽  
Kinetics Of

The kinetics of passive transport of ketoprofen and metformin, as model substances for high and low permeability, respectively, across the artificial membrane under the influence of the pH of donor solution was investigated. There was an upward trend in the apparent permeation coefficient (Papp) of ketoprofen with the decrease in pH to a value close to pKa. At the pH value below pKa the permeation coefficient had lower value, due to the higher retention of ketoprofen in the artificial membrane. Metformin is a low permeable compound, and the highest permeation values were recorded at pH 7.4. Two dissociation constants determine that metformin at physiological pH exists as a hydrophilic cationic molecule, i.e. predominantly in ionized form. At pH values below 2.8, metformin mainly exists in diprotonated form, and it was, thus, very poorly permeable. The highest retention, i.e. affinity of both ketoprofen and metformin to the membrane, was at the lowest pH values, which is explained by different mechanisms. At higher pH values of the donor compartment, the substances showed significantly less affinity to the membrane. The obtained values of apparent permeation coefficients at studied pH values showed a good correlation with the obtained experimental values by other in vitro methods.    

Cyanide binding to canine myeloperoxidase

1989 ◽  
Vol 67 (4-5) ◽  
pp. 187-191 ◽  
Author(s):  
Leah A. Marquez ◽  
H. Brian Dunford
Keyword(s):  
Rate Constant ◽  
Binding Sites ◽  
Ph Dependence ◽  
Order Rate Constant ◽  
Protonated Form ◽  
Isosbestic Point ◽  
Equilibrium Binding ◽  
Cyanide Binding ◽  
Kinetics Of ◽  
Base Group

Equilibria and kinetics of cyanide binding to canine myeloperoxidase were studied. Spectral results support the presence of two heme binding sites; an isosbestic point at 444 nm and a linear Scatchard plot suggest that the binding affinity of cyanide to the two subunits of the enzyme is the same. The dissociation constant is 0.53 μM. The pH dependence of the apparent second order rate constant indicates the presence of an acid–base group on the enzyme with a pKa of 3.8 ± 0.1. The protonated form of cyanide binds to the basic enzyme with a rate constant of (4.3 ± 0.3) × 106 M−1 s−1.Key words: myeloperoxidase, cyanide binding, equilibrium binding, ligand binding kinetics.

Influence of Brain Gangliosides on the Formation and Properties of Supported Lipid Bilayers for Binding Kinetics Studies

2018 ◽  
Author(s):  
Luke Jordan ◽  
Nathan Wittenberg
Keyword(s):  
Lipid Bilayers ◽  
Binding Kinetics ◽  
Supported Lipid Bilayers ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Supported Lipid Bilayer ◽  
Head Groups ◽  
Lipid Diffusion ◽  
Kinetics Of ◽  
Brain Gangliosides

This is a comprehensive study of the effects of the four major brain gangliosides (GM1, GD1b, GD1a, and GT1b) on the adsorption and rupture of phospholipid vesicles on SiO2 surfaces for the formation of supported lipid bilayer (SLB) membranes. Using quartz crystal microbalance with dissipation monitoring (QCM-D) we show that gangliosides GD1a and GT1b significantly slow the SLB formation process, whereas GM1 and GD1b have smaller effects. This is likely due to the net ganglioside charge as well as the positions of acidic sugar groups on ganglioside glycan head groups. Data is included that shows calcium can accelerate the formation of ganglioside-rich SLBs. Using fluorescence recovery after photobleaching (FRAP) we also show that the presence of gangliosides significantly reduces lipid diffusion coefficients in SLBs in a concentration-dependent manner. Finally, using QCM-D and GD1a-rich SLB membranes we measure the binding kinetics of an anti-GD1a antibody that has similarities to a monoclonal antibody that is a hallmark of a variant of Guillain-Barre syndrome.

Rationalizing the pH-Activity Response for Escherichia Coli’s Glycinamide Ribonucleotidetransformylase Through Computational Methods

2019 ◽  
Author(s):  
Adrian Roitberg ◽  
Pancham Lal Gupta
Keyword(s):  
Transfer Reaction ◽  
Catalytic Mechanism ◽  
Ph Dependence ◽  
Ph Effects ◽  
Dependent Manner ◽  
E Coli ◽  
Gar Tfase ◽  
Activity Curve ◽  
Ph Dependent ◽  
Formyl Transfer

<div>Human Glycinamide ribonucleotide transformylase (GAR Tfase), a regulatory enzyme in the de novo purine biosynthesis pathway, has been established as an anti-cancer target. GAR Tfase catalyzes the formyl transfer reaction from the folate cofactor to the GAR ligand. In the present work, we study E. coli GAR Tfase, which has high sequence similarity with the human GAR Tfase with most functional residues conserved. E. coli GAR Tfase exhibits structural changes and the binding of ligands that varies with pH which leads to change the rate of the formyl transfer reaction in a pH-dependent manner. Thus, the inclusion of pH becomes essential for the study of its catalytic mechanism. Experimentally, the pH-dependence of the kinetic parameter kcat is measured to evaluate the pH-range of enzymatic activity. However, insufficient information about residues governing the pH-effects on the catalytic activity leads to ambiguous assignments of the general acid and base catalysts and consequently its catalytic mechanism. In the present work, we use pH-replica exchange molecular dynamics (pH-REMD) simulations to study the effects of pH on E. coli GAR Tfase enzyme. We identify the titratable residues governing the pH-dependent conformational changes in the system. Furthermore, we filter out the protonation states which are essential in maintaining the structural integrity, keeping the ligands bound and assisting the catalysis. We reproduce the experimental pH-activity curve by computing the population of key protonation states. Moreover, we provide a detailed description of residues governing the acidic and basic limbs of the pH-activity curve.</div>

Adsorption Equilibrium and Kinetics of CO2 and H2O on Activated Carbon

2012 ◽  
Vol 27 (2) ◽  
pp. 139-145 ◽  
Author(s):  
Dong XU ◽  
Jun ZHANG ◽  
Gang LI ◽  
Penny XIAO ◽  
Paul WEBLEY ◽  
...  
Keyword(s):  
Activated Carbon ◽  
Adsorption Equilibrium ◽  
Equilibrium And Kinetics ◽  
Adsorption Equilibrium And Kinetics ◽  
Kinetics Of
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