scholarly journals Binding to thermolysin of phenolate-containing inhibitors necessitates a revised mechanism of catalysis

1994 ◽  
Vol 302 (1) ◽  
pp. 57-68 ◽  
Author(s):  
W L Mock ◽  
M Aksamawati
Keyword(s):  
Metal Ion ◽  
Competitive Inhibition ◽  
Solvent Molecule ◽  
Bound Water ◽  
Amide Bond ◽  
Lewis Acidity ◽  
Ph Profile ◽  
Binding Characteristics ◽  
Ph Values ◽  
Mechanism Of Catalysis

Competitive inhibition as a function of pH for the metalloendoprotease thermolysin by derivatives of L-alpha-(2-hydroxyphenyl)benzenepropanoyl-L- tryptophanylglycylglycine exhibits a diagnostic bell shape. Binding is maximal between two pKa values: on the acidic limb the apparent Ki value is regulated by an unchanging enzymic ionization (pKa 5.3) which is also seen in the substrate-hydrolysis kinetics (kcat/Km), whereas the alkaline limb for inhibition varies and depends specifically on the pKa of the phenolic group in the inhibitor. Although it should be the phenolate form of the inhibitor that co-ordinates more efficiently to the active-site Zn2+, the apparent Ki shifts from pH-independent at pH values immediately below the inhibitor's pKa to progressively weaker binding at higher pH. This is explained by an anomalous acidity for the exchangeable solvent molecule that is attached to enzymic Zn2+ in the absence of substrate or inhibitor. Since OH- cannot be displaced from the enzyme as readily as H2O, a compensating pKa of 5.3 possessed by Zn(2+)-bound water rationalizes the binding characteristics, yielding the level pH profile exhibited at intermediate pH values. Recognition of the implicit heightened Lewis acidity of the metal ion in thermolysin leads to a revision of the mechanism of catalysis. The substrate amide bond becomes activated for hydrolysis by carbonyl-group co-ordination to the especially acidic Zn2+ ion (completely displacing the H2O/OH- species otherwise bound). The imidazole group of enzymic residue His-231, also discerned in the pH profile for kcat/Km from its pKa of 8, provides general-base assistance for hydration of the activated scissile linkage in the first committed step of catalysis. Additional evidence from inhibition patterns shows how substrate-binding energy may be employed in this scheme to promote hydrolysis of peptides by thermolysin.

scholarly journals Fluxionate Lewis acidity of the Zn2+ ion in carboxypeptidase A

1993 ◽  
Vol 289 (1) ◽  
pp. 185-193 ◽  
Author(s):  
W L Mock ◽  
D J Freeman ◽  
M Aksamawati
Keyword(s):  
Metal Ion ◽  
Competitive Inhibition ◽  
Dissociation Constants ◽  
Ph Dependence ◽  
Bound Water ◽  
Acid Dissociation ◽  
Lewis Acidity ◽  
Carboxypeptidase A ◽  
A Value ◽  
Straight Line

Competitive inhibition constants Ki for a series of phenol-ring-substituted derivatives of alpha-(2-hydroxyphenyl)benzenepropanoic acid have been ascertained by observing their influence on the catalytic hydrolysis of a peptide substrate by the zinc enzyme carboxypeptidase A. The pH-dependence of Ki shows that binding is maximal between two pKa values: one is that of the phenol group of the inhibitor, and the other uniformly has a value of 6, the pKa of a Zn(2+)-bound water molecule on the enzyme in the absence of substrate or inhibitor. This is the dependence expected if phenolate binds to the Zn2+ displacing its bound H2O/HO-. A log-log plot of the dissociation constants for the productive forms of inhibitor plus enzyme versus the acid dissociation constants of the phenolic residues in the inhibitors yields a straight line with a slope of +0.76. This number indicates that the active-site metal ion has special capacity for dispersing negative charge, such as builds up on the oxygen atom of a carboxamide group undergoing nucleophilic addition.

scholarly journals Pyrene Carboxylate Ligand Based Coordination Polymers for Microwave-Assisted Solvent-Free Cyanosilylation of Aldehydes

Molecules ◽  
2021 ◽  
Vol 26 (4) ◽  
pp. 1101
Author(s):  
Anirban Karmakar ◽  
Anup Paul ◽  
Elia Pantanetti Sabatini ◽  
M. Fátima C. Guedes da Silva ◽  
Armando J. L. Pombeiro
Keyword(s):  
Coordination Polymer ◽  
Single Crystal ◽  
Coordination Polymers ◽  
Metal Ion ◽  
Solvent Free ◽  
Lewis Acidity ◽  
Carboxylate Ligand ◽  
X Ray Diffraction ◽  
X Ray ◽  
Microwave Assisted

The new coordination polymers (CPs) [Zn(μ-1κO1:1κO2-L)(H2O)2]n·n(H2O) (1) and [Cd(μ4-1κO1O2:2κN:3,4κO3-L)(H2O)]n·n(H2O) (2) are reported, being prepared by the solvothermal reactions of 5-{(pyren-4-ylmethyl)amino}isophthalic acid (H2L) with Zn(NO3)2.6H2O or Cd(NO3)2.4H2O, respectively. They were synthesized in a basic ethanolic medium or a DMF:H2O mixture, respectively. These compounds were characterized by single-crystal X-ray diffraction, FTIR spectroscopy, thermogravimetric and elemental analysis. The single-crystal X-ray diffraction analysis revealed that compound 1 is a one dimensional linear coordination polymer, whereas 2 presents a two dimensional network. In both compounds, the coordinating ligand (L2−) is twisted due to the rotation of the pyrene ring around the CH2-NH bond. In compound 1, the Zn(II) metal ion has a tetrahedral geometry, whereas, in 2, the dinuclear [Cd2(COO)2] moiety acts as a secondary building unit and the Cd(II) ion possesses a distorted octahedral geometry. Recently, several CPs have been explored for the cyanosilylation reaction under conventional conditions, but microwave-assisted cyanosilylation of aldehydes catalyzed by CPs has not yet been well studied. Thus, we have tested the solvent-free microwave-assisted cyanosilylation reactions of different aldehydes, with trimethylsilyl cyanide, using our synthesized compounds, which behave as highly active heterogeneous catalysts. The coordination polymer 1 is more effective than 2, conceivably due to the higher Lewis acidity of the Zn(II) than the Cd(II) center and to a higher accessibility of the metal centers in the former framework. We have also checked the heterogeneity and recyclability of these coordination polymers, showing that they remain active at least after four recyclings.

scholarly journals Liquid-liquid extraction and facilitated membrane transport of Pb2+ using a lipophilic acridono-crown ether as carrier

2020 ◽  
Vol 99 (1-2) ◽  
pp. 117-129
Author(s):  
Ádám Golcs ◽  
László Bezúr ◽  
Péter Huszthy ◽  
Tünde Tóth
Keyword(s):  
Membrane Transport ◽  
Metal Ion ◽  
Liquid Membrane ◽  
Competitive Inhibition ◽  
Liquid Extraction ◽  
Bulk Liquid ◽  
Bulk Liquid Membrane ◽  
Liquid Liquid Extraction ◽  
Component Systems ◽  
Source Phase

AbstractStudies on liquid-liquid extraction and bulk liquid membrane (BLM) technique-based metal ion separation by a previously published Pb2+-selective acridono-18-crown-6 ether selector molecule were performed. The effects of the stirring speed, the quality of apolar organic membrane, the counterions of Pb2+, the pH of the aqueous phase, the concentration of the source phase, the concentration of the carrier in the BLM and the temperature on the Pb2+-separation were investigated. Moreover, the effects of the competitive inhibition due to the presence of Ag+, Ca2+, Co2+, Cu2+, K+, Mg2+, Na+ and Zn2+ as competing ions in a multicomponent aqueous source phase of different ion-concentrations were also studied. After a proper dilution of the multicomponent aqueous source phase, excellent Pb2+-selectivity was achieved without a significant reduction in the efficiency compared to the liquid membrane transport of single-component systems. Based on the BLM-cell studies the applied selector molecule proved to be suitable for the development of liquid membrane-based Pb2+-selective separation methods, which can be greatly aided by the analysis of the effects on the separation and by the optimization of the parameters of the process discussed here.

scholarly journals Mechanism of Coagulation of Humic Acid in Presence of Metal Ion Coagulants at Low pH Values

1970 ◽  
Vol 73 (5) ◽  
pp. 874-878 ◽  
Author(s):  
Takao YOTSUYANAGI ◽  
Katsumi GOTO ◽  
Masaichi NAGAYAMA
Keyword(s):  
Humic Acid ◽  
Metal Ion ◽  
Low Ph ◽  
Ph Values

The aquation of cis-Chlorodi(methyl sulphoxide)bisethylenediaminecobalt(III), cis-Chlorodimethylformamidebisethylenediaminecobalt(III), and cis-Chlorodimethylacetamidebisethylenediaminecobalt(III) ions

1966 ◽  
Vol 19 (10) ◽  
pp. 1821 ◽  
Author(s):  
IR Lantzke ◽  
DW Watts
Keyword(s):  
Solvent Molecule ◽  
Chloride Ion ◽  
Side Reaction ◽  
Base Hydrolysis ◽  
Alkaline Solutions ◽  
Replacement Reaction ◽  
Ph Values ◽  
Trigonal Bipyramidal ◽  
Entropy Of Activation ◽  
Solvent Replacement

The aquation of each of three octahedral chloro(solvent)bisethylene- diaminecobalt(III) ions, involving the solvent ligands dimethyl sulphoxide (DMSO), dimethylformamide (DMF), and dimethylacetamide (DMA), has been examined in solutions of different pH. In solutions of pH less than 6, the predominant reaction is replacement of the solvent molecule by water in an SN1 process, involving a trigonal bipyramidal transition state and resulting in a mixture of the trans- and cis- chloroaquo complexes. The slow loss of chloride ion is an accompanying side reaction. In solutions of pH greater than 6 base hydrolysis becomes important, and in alkaline solutions the rate of solvent loss is too fast to measure by conventional techniques. The rate of liberation of chloride ion is also greatly increased with increasing pH. Values of the activation energy, and entropy of activation, are reported for the solvent replacement reaction at a pH of 1.90.

scholarly journals Crystal structures of four dimeric manganese(II) bromide coordination complexes with various derivatives of pyridine N-oxide

2019 ◽  
Vol 75 (8) ◽  
pp. 1284-1290
Author(s):  
Sheridan Lynch ◽  
Genevieve Lynch ◽  
Will E. Lynch ◽  
Clifford W. Padgett
Keyword(s):  
Hydrogen Bonding ◽  
Solvent Molecule ◽  
Bound Water ◽  
Manganese Atom ◽  
Coordination Complexes ◽  
Water Molecules ◽  
Inversion Center ◽  
Dimeric Complex ◽  
Bromide Ions ◽  
Derivatives Of

Four manganese(II) bromide coordination complexes have been prepared with four pyridine N-oxides, viz. pyridine N-oxide (PNO), 2-methylpyridine N-oxide (2MePNO), 3-methylpyridine N-oxide (3MePNO), and 4-methylpyridine N-oxide (4MePNO). The compounds are bis(μ-pyridine N-oxide)bis[aquadibromido(pyridine N-oxide)manganese(II)], [Mn2Br4(C5H5NO)4(H2O)2] (I), bis(μ-2-methylpyridine N-oxide)bis[diaquadibromidomanganese(II)]–2-methylpyridine N-oxide (1/2), [Mn2Br4(C6H7NO)2(H2O)4]·2C6H7NO (II), bis(μ-3-methylpyridine N-oxide)bis[aquadibromido(3-methylpyridine N-oxide)manganese(II)], [Mn2Br4(C6H7NO)4(H2O)2] (III), and bis(μ-4-methylpyridine N-oxide)bis[dibromidomethanol(4-methylpyridine N-oxide)manganese(II)], [Mn2Br4(C6H7NO)4(CH3OH)2] (IV). All the compounds have one unique MnII atom and form a dimeric complex that contains two MnII atoms related by a crystallographic inversion center. Pseudo-octahedral six-coordinate manganese(II) centers are found in all four compounds. All four compounds form dimers of Mn atoms bridged by the oxygen atom of the PNO ligand. Compounds I, II and III exhibit a bound water of solvation, whereas compound IV contains a bound methanol molecule of solvation. Compounds I, III and IV exhibit the same arrangement of molecules around each manganese atom, ligated by two bromide ions, oxygen atoms of two PNO ligands and one solvent molecule, whereas in compound II each manganese atom is ligated by two bromide ions, one O atom of a PNO ligand and two water molecules with a second PNO molecule interacting with the complex via hydrogen bonding through the bound water molecules. All of the compounds form extended hydrogen-bonding networks, and compounds I, II, and IV exhibit offset π-stacking between PNO ligands of neighboring dimers.

scholarly journals Surface Epitope Coverage Affects Binding Characteristics of Bisphenol-A Functionalized Nanoparticles in a Competitive Inhibition Assay

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Yang Lu ◽  
Joshua Richard Peterson ◽  
Erwann Luais ◽  
John Justin Gooding ◽  
Nanju Alice Lee
Keyword(s):  
Bisphenol A ◽  
Binding Sites ◽  
Competitive Inhibition ◽  
Limit Of Detection ◽  
Molar Concentration ◽  
Inhibition Assay ◽  
Binding Characteristics ◽  
Sensor Performance ◽  
Reliable Detection ◽  
Minimum Number

The biomolecule interface is a key element in immunosensor fabrication, which can greatly influence the sensor performance. This paper explores the effects of surface epitope coverage of small molecule functionalized nanoparticle on the apparent affinity (avidity) of antibody in a competitive inhibition assay using bisphenol-A (BPA) as a model target. An unconventional two-antibody competitive inhibition ELISA (ci-ELISA) using thiolated BPA modified gold nanoparticles (cysBPAv-AuNP) as a competing reagent was devised for this study. It was shown that the antibody complexation with cysBPAv-AuNPs required a minimum number of surface epitopes on the nanoparticle to form a sufficiently strong interaction and reliable detection. The binding of cysBPAv-AuNP to anti-BPA antibodies, for limited antibody binding sites, was enhanced by a greater number of epitope-modified nanoparticles (cysBPAv-AuNP) as well as with higher epitope coverage. Increasing the molar concentration of epitope present in an assay enhanced the binding between anti-BPA antibodies and cysBPAv-AuNP. This implies that, to increase the limit of detection of a competitive inhibition assay, a reduced molar concentration of epitope should be applied. This could be achieved by either lowering the epitope coverage on each cysBPAv-AuNP or the assay molar concentration of cysBPAv-AuNP or both of these factors.

scholarly journals Antibodies against Thrombospondin-Related Anonymous Protein Do Not Inhibit Plasmodium Sporozoite Infectivity In Vivo

2000 ◽  
Vol 68 (6) ◽  
pp. 3667-3673 ◽  
Author(s):  
Soren Gantt ◽  
Cathrine Persson ◽  
Keith Rose ◽  
Ashley J. Birkett ◽  
Ruben Abagyan ◽  
...  
Keyword(s):  
Metal Ion ◽  
Competitive Inhibition ◽  
Polyclonal Antibodies ◽  
Three Dimensional ◽  
Calcium Ionophore ◽  
Plasmodium Yoelii ◽  
Gliding Motility ◽  
Vaccine Antigen ◽  
Dimensional Structure

ABSTRACT Thrombospondin-related anonymous protein (TRAP), a candidate malaria vaccine antigen, is required for Plasmodiumsporozoite gliding motility and cell invasion. For the first time, the ability of antibodies against TRAP to inhibit sporozoite infectivity in vivo is evaluated in detail. TRAP contains an A-domain, a well-characterized adhesive motif found in integrins. We modeled here a three-dimensional structure of the TRAP A-domain of Plasmodium yoelii and located regions surrounding the MIDAS (metal ion-dependent adhesion site), the presumed business end of the domain. Mice were immunized with constructs containing these A-domain regions but were not protected from sporozoite challenge. Furthermore, monoclonal and rabbit polyclonal antibodies against the A-domain, the conserved N terminus, and the repeat region of TRAP had no effect on the gliding motility or sporozoite infectivity to mice. TRAP is located in micronemes, secretory organelles of apicomplexan parasites. Accordingly, the antibodies tested here stained cytoplasmic TRAP brightly by immunofluorescence. However, very little TRAP could be detected on the surface of sporozoites. In contrast, a dramatic relocalization of TRAP onto the parasite surface occurred when sporozoites were treated with calcium ionophore. This likely mimics the release of TRAP from micronemes when a sporozoite contacts its target cell in vivo. Contact with hepatoma cells in culture also appeared to induce the release of TRAP onto the surface of sporozoites. If large amounts of TRAP are released in close proximity to its cellular receptor(s), effective competitive inhibition by antibodies may be difficult to achieve.

scholarly journals The nonenzymatic template-directed ligation of oligonucleotides

2006 ◽  
Vol 3 (3) ◽  
pp. 243-249 ◽  
Author(s):  
A. V. Lutay ◽  
E. L. Chernolovskaya ◽  
M. A. Zenkova ◽  
V. V. Vlassov
Keyword(s):  
Metal Ion ◽  
Divalent Cations ◽  
Bound Water ◽  
Transesterification Reaction ◽  
Water Molecules ◽  
Pka Values ◽  
Rna Molecules ◽  
High Reaction ◽  
Cyclic Phosphate ◽  
Cyclic Phosphates

Abstract. The nonenzymatic template-directed ligation of oligonucleotides containing 2', 3'-cyclic phosphate was investigated in the presence of divalent cations. Ligation of the oligonucleotides readily occurred in the presence of Mg2+, Mn2+, Co2+, Zn2+, Pb2+. Efficacy of the metal ion catalysts inversely correlated with pKa values of the metal-bound water molecules. The intermolecular transesterification reaction yielded at least 95metal ion. Relatively high reaction yields (up to 15fragmentation to oligonucleotides with 2',3'-cyclic phosphates, followed by reactions of those oligonucleotides could provide a source of new RNA molecules under prebiotic conditions.

Sign in / Sign up

Export Citation Format

Share Document