Activation and inactivation of acetylcholinesterase by metal ions

1981 ◽  
Vol 59 (9) ◽  
pp. 728-735 ◽  
Author(s):  
George Tomlinson ◽  
Bulent Mutus ◽  
Ian McLennan
Keyword(s):  
Ionic Strength ◽  
Metal Ions ◽  
Metal Ion ◽  
Prolonged Exposure ◽  
Chelating Agent ◽  
High Ionic Strength ◽  
Metal Ion Binding ◽  
Peripheral Site ◽  
Metal Ion Effects ◽  
Low Ionic Strength

The kinetic consequences of acetylcholinesterase peripheral site occupation by metal ions were examined using three substrates; acetylthiocholine, p-nitrophenylacetate, and 7-(dimethylcarbamoyloxy)-N-methylquinolinium iodide. Two classes of metal ion effects were noted: activation by a group including Mg2+, Ca2+, Mn2+, and Na+, and inactivation by a second group which to date includes Zn2+, Cd2+, Hg2+, Ni2+, Cu2+, and Pb2+. Activation is demonstrable only in solutions of low ionic strength whereas inactivation can be readily observed in solutions of both low and high ionic strength. Activation appears to be due to a combination of metal ion binding and ionic strength effects and involves binding to peripheral sites which are distinct from those which bind organic cationic activators such as gallamine, propidium, and 7-(dimethylcarbamoyloxy)-N-methylquinolinium. The principal activating effect is on the deacylation phase of the enzyme–substrate reaction. Inactivators effect a slow conversion of the enzyme to an unreactive form. The kinetics of inactivation are biphasic at low ionic strength but become essentially monophasic at high ionic strength. More than 80% of the enzyme activity can be recovered upon addition of EDTA provided the chelating agent is added immediately following completion of the inactivation process. Prolonged exposure to inactivators results in a progressive decrease in the amount of recoverable activity. Although peripheral ligand interactions may result in a variety of catalytic site conformations, the macroscopic properties can be accounted for in terms of three ligand-dependent states of the enzyme in which catalytic ability (actual or potential) is retained, and a fourth denatured state.

scholarly journals Emulsifying and Metal Ion Binding Activity of a Glycoprotein Exopolymer Produced by Pseudoalteromonas sp. Strain TG12

2008 ◽  
Vol 74 (15) ◽  
pp. 4867-4876 ◽  
Author(s):  
Tony Gutierrez ◽  
Tracy Shimmield ◽  
Cheryl Haidon ◽  
Kenny Black ◽  
David H. Green
Keyword(s):  
Ionic Strength ◽  
Marine Sediment ◽  
Metal Ion ◽  
Chelating Agent ◽  
Binding Activity ◽  
Metal Species ◽  
Metal Ion Binding ◽  
New Class ◽  
Isolation And Characterization ◽  
Ecological Aspects

ABSTRACT In this study, we describe the isolation and characterization of a new exopolymer that exhibits high emulsifying activities against a range of oil substrates and demonstrates a differential capacity to desorb various mono-, di-, and trivalent metal species from marine sediment under nonionic and seawater ionic-strength conditions. This polymer, PE12, was produced by a new isolate, Pseudoalteromonas sp. strain TG12 (accession number EF685033), during growth in a modified Zobell's 2216 medium amended with 1% glucose. Chemical and chromatographic analysis showed it to be a high-molecular-mass (>2,000 kDa) glycoprotein composed of carbohydrate (32.3%) and protein (8.2%). PE12 was notable in that it contained xylose as the major sugar component at unusually high levels (27.7%) not previously reported for a Pseudoalteromonas exopolymer. The polymer was shown to desorb various metal species from marine sediment—a function putatively conferred by its high content of uronic acids (28.7%). Seawater ionic strength (simulated using 0.6 M NaCl), however, caused a significant reduction in PE12's ability to desorb the sediment-adsorbed metals. These results demonstrate the importance of electrolytes, a physical parameter intrinsic of seawater, in influencing the interaction of microbial exopolymers with metal ions. In summary, PE12 may represent a new class of Pseudoalteromonas exopolymer with a potential for use in biotechnological applications as an emulsifying or metal-chelating agent. In addition to the biotechnological potential of these findings, the ecological aspects of this and related bacterial exopolymers in marine environments are also discussed.

scholarly journals Effect of bivalent cations on the adenosine triphosphatase of actomyosin and its modification by tropomyosin and troponin

1969 ◽  
Vol 111 (5) ◽  
pp. 777-783 ◽  
Author(s):  
M. C. Schaub ◽  
M. Ermini
Keyword(s):  
Ionic Strength ◽  
Metal Ions ◽  
Metal Ion ◽  
Adenosine Triphosphatase ◽  
Ionic Radius ◽  
Unique Feature ◽  
Optimum Concentration ◽  
Adenosine Triphosphatase Activity ◽  
Bivalent Cations ◽  
Low Ionic Strength

1. After removal of tropomyosin and troponin from the ‘natural’ actomyosin complex, the adenosine triphosphatase activity of the resulting ‘desensitized’ actomyosin is stimulated to the same extent by various bivalent cations with an ionic radius in the range 0·65–0·99å when tested at optimum concentration of the metal ion in the presence of 2·5mm-ATP at low ionic strength and pH7·6. Under identical conditions the adenosine triphosphatase activity of myosin alone is stimulated to an appreciable extent only by Ca2+ (ionic radius 0·99å). 2. Tropomyosin narrows the range of size of the stimulatory cations by inhibiting specifically the adenosine triphosphatase activity of ‘desensitized’ actomyosin when stimulated by Ca2+ or the slightly smaller Cd2+ (ionic radius 0·97å). Tropomyosin has no effect on the adenosine triphosphatase activity of ‘desensitized’ actomyosin when stimulated by the smaller cations, nor on the Ca2+-activated adenosine triphosphatase activity of myosin alone. 3. The adenosine triphosphatase activity of the ‘natural’ actomyosin system (containing tropomyosin and troponin) stimulated by the smallest cation, Mg2+ (ionic radius 0·65å), is low when the system is deprived of Ca2+ but high in the presence of small amounts of Ca2+. This sensitivity to Ca2+ seems to be a unique feature of the Mg2+-stimulated system. 4. The changes in specificity of the myosin adenosine triphosphatase activity in its requirement for bivalent cations caused by interaction with actin, tropomyosin and troponin primarily concern the size of the metal ions. The effects on enzymic properties of myofibrils due to tropomyosin and troponin can be demonstrated at low and at physiological ionic strength.

The influence of metal-ion binding on the structure and surface composition of Sonic Hedgehog: a combined classical and hybrid QM/MM MD study

2016 ◽  
Vol 18 (32) ◽  
pp. 22254-22265 ◽  
Author(s):  
Manuel Hitzenberger ◽  
Thomas S. Hofer
Keyword(s):  
Metal Ions ◽  
Sonic Hedgehog ◽  
Binding Sites ◽  
Metal Ion ◽  
Surface Composition ◽  
Quantum Mechanical ◽  
Ion Binding ◽  
Metal Ion Binding ◽  
Structural Impact

The interaction of metal ions with Shh binding-sites and their structural impact are assessed via classical and quantum mechanical simulations.

scholarly journals Functional characterization of the dimerization domain of the ferric uptake regulator (Fur) of Pseudomonas aeruginosa

2006 ◽  
Vol 400 (3) ◽  
pp. 385-392 ◽  
Author(s):  
Erdeni Bai ◽  
Federico I. Rosell ◽  
Bao Lige ◽  
Marcia R. Mauk ◽  
Barbara Lelj-Garolla ◽  
...  
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Metal Ions ◽  
Binding Site ◽  
Metal Ion ◽  
Association Constants ◽  
Ion Binding ◽  
Ferric Uptake Regulator ◽  
Metal Ion Binding ◽  
Dimerization Domain ◽  
High Affinity

The functional properties of the recombinant C-terminal dimerization domain of the Pseudomonas aeruginosa Fur (ferric uptake regulator) protein expressed in and purified from Escherichia coli have been evaluated. Sedimentation velocity measurements demonstrate that this domain is dimeric, and the UV CD spectrum is consistent with a secondary structure similar to that observed for the corresponding region of the crystallographically characterized wild-type protein. The thermal stability of the domain as determined by CD spectroscopy decreases significantly as pH is increased and increases significantly as metal ions are added. Potentiometric titrations (pH 6.5) establish that the domain possesses a high-affinity and a low-affinity binding site for metal ions. The high-affinity (sensory) binding site demonstrates association constants (KA) of 10(±7)×106, 5.7(±3)×106, 2.0(±2)×106 and 2.0(±3)×104 M−1 for Ni2+, Zn2+, Co2+ and Mn2+ respectively, while the low-affinity (structural) site exhibits association constants of 1.3(±2)×106, 3.2(±2)×104, 1.76(±1)×105 and 1.5(±2)×103 M−1 respectively for the same metal ions (pH 6.5, 300 mM NaCl, 25 °C). The stability of metal ion binding to the sensory site follows the Irving–Williams order, while metal ion binding to the partial sensory site present in the domain does not. Fluorescence experiments indicate that the quenching resulting from binding of Co2+ is reversed by subsequent titration with Zn2+. We conclude that the domain is a reasonable model for many properties of the full-length protein and is amenable to some analyses that the limited solubility of the full-length protein prevents.

scholarly journals Crystallographic and X-ray absorption spectroscopic characterization of Helicobacter pylori UreE bound to Ni2+ and Zn2+ reveals a role for the disordered C-terminal arm in metal trafficking

2012 ◽  
Vol 441 (3) ◽  
pp. 1017-1035 ◽  
Author(s):  
Katarzyna Banaszak ◽  
Vlad Martin-Diaconescu ◽  
Matteo Bellucci ◽  
Barbara Zambelli ◽  
Wojciech Rypniewski ◽  
...  
Keyword(s):  
Helicobacter Pylori ◽  
Metal Ions ◽  
Metal Binding ◽  
Metal Ion ◽  
Mutual Influence ◽  
Accurate Information ◽  
Metal Ion Binding ◽  
X Ray ◽  
X Ray Absorption

The survival and growth of the pathogen Helicobacter pylori in the gastric acidic environment is ensured by the activity of urease, an enzyme containing two essential Ni2+ ions in the active site. The metallo-chaperone UreE facilitates in vivo Ni2+ insertion into the apoenzyme. Crystals of apo-HpUreE (H. pylori UreE) and its Ni2+- and Zn2+-bound forms were obtained from protein solutions in the absence and presence of the metal ions. The crystal structures of the homodimeric protein, determined at 2.00 Å (apo), 1.59 Å (Ni2+) and 2.52 Å (Zn2+) resolution, show the conserved proximal and solvent-exposed His102 residues from two adjacent monomers invariably involved in metal binding. The C-terminal regions of the apoprotein are disordered in the crystal, but acquire significant ordering in the presence of the metal ions due to the binding of His152. The analysis of X-ray absorption spectral data obtained using solutions of Ni2+- and Zn2+-bound HpUreE provided accurate information of the metal-ion environment in the absence of solid-state effects. These results reveal the role of the histidine residues at the protein C-terminus in metal-ion binding, and the mutual influence of protein framework and metal-ion stereo-electronic properties in establishing co-ordination number and geometry leading to metal selectivity.

Bromine substituted aminonaphthoquinones: synthesis, characterization, DFT and metal ion binding studies

RSC Advances ◽  
2016 ◽  
Vol 6 (91) ◽  
pp. 88010-88029 ◽  
Author(s):  
Gunjan Agarwal ◽  
Dipali N. Lande ◽  
Debamitra Chakrovarty ◽  
Shridhar P. Gejji ◽  
Prajakta Gosavi-Mirkute ◽  
...  
Keyword(s):  
Metal Ions ◽  
Metal Ion ◽  
Ion Binding ◽  
Metal Ion Binding ◽  
Binding Studies

Bromine substituted aminonaphthoquinones – chemosensors for metal ions.

Comparison between specific surface complexation and Donnan ion-exchange models for describing the adsorption of cations on kraft fibres – literature evidence and EXAFS study of Cu(II) binding

2010 ◽  
Vol 25 (2) ◽  
pp. 178-184 ◽  
Author(s):  
Ola Sundman ◽  
Per Persson ◽  
Lars-Olof Öhman
Keyword(s):  
Ionic Strength ◽  
Ion Exchange ◽  
Metal Ion ◽  
Experimental Conditions ◽  
Cellulose Fibres ◽  
Metal Ion Adsorption ◽  
Literature Evidence ◽  
Trivalent Cations ◽  
Exafs Study ◽  
Low Ionic Strength

Abstract A compilation of the applied experimental conditions when studying metal ion adsorption onto kraft fibres, and the resulting conclusion, revealed that the ionic strength conditions used during the experiments were an important dividing factor. At low ionic strengths, the conclusion has regularly been that the Donnan ion-exchange model could correctly predict the adsorption while, at higher ionic strengths, it has often been concluded that the formation of specific metal-ion fibre complexes must be assumed. To study this apparent influence from the presence of monovalent sodium ions, Cu K-edge EXAFS spectra of Cu2+ ions adsorbed to kraft fibres were collected in media of “0” to 100 mM NaCl. Combined with previous data, these measurements confirmed that at very low ionic strength, the importance of specific interactions between the chemically modified cellulose fibres and the Cu(II) ions significantly decreased. For a detailed description of the adsorption phenomenon, both types of interactions must be considered simultaneously. For most technical and engineering applications, however, the Donnan model can be used at low ionic strength conditions, i.e. I ≲ 10 mM. At higher ionic strengths, though, the inclusion of specific complexes in the model is necessary for correctly describing the adsorption of di- and trivalent cations with strong complex forming properties.

Synthesis, photophysics, electrochemistry and metal ion-binding studies of rhenium(i) complexes with crown ether pendants: selective and specific binding properties for various metal ions

2005 ◽  
Vol 29 (1) ◽  
pp. 165 ◽  
Author(s):  
Keith Man-Chung Wong ◽  
Wei-Ping Li ◽  
Kung-Kai Cheung ◽  
Vivian Wing-Wah Yam
Keyword(s):  
Crown Ether ◽  
Metal Ions ◽  
Metal Ion ◽  
Specific Binding ◽  
Ion Binding ◽  
Metal Ion Binding ◽  
Binding Studies ◽  
Binding Properties

scholarly journals Multiple supramolecular structures formed by interaction of actin with protamine

1982 ◽  
Vol 205 (1) ◽  
pp. 31-37 ◽  
Author(s):  
Enrico Grazi ◽  
Ermes Magri ◽  
Ivonne Pasquali-Ronchetti
Keyword(s):  
Ionic Strength ◽  
Exchange Reaction ◽  
Dead Time ◽  
High Ionic Strength ◽  
Supramolecular Structures ◽  
Molar Ratio ◽  
First Case ◽  
Atpase Reaction ◽  
Low Ionic Strength ◽  
Millipore Filters

When protamine is added to actin, different supramolecular structures are formed depending on the molar ratio of the two proteins and of the ionic strength of the medium. At low ionic strength, and going from a molar ratio of protamine to G-actin of 4:1, 2:1 and 1:1, globular aggregates are first converted into extended structures and then to long threads in which the constituent ATP–G-actin is rapidly exchangeable with the actin of the medium. At high ionic strength {Tyrode [(1910) Arch. Int. Pharmacodyn. Ther.20, 205–212] solution}, starting from G-actin and protamine in the 1:1 molar ratio, long ropes are formed that can be resolved into intertwining filaments of 4–5nm diameter. The addition of protamine in a 1:1 molar ratio to a solution of F-actin in Tyrode solution causes the breakage of the actin filaments, which is also revealed by the decrease of the viscosity of the solution and the formation of ordered latero-lateral aggregates. The structures formed by reaction of protamine with G-actin can be separated from free G-actin and protamine by filtration through 0.45μm-pore-size Millipore filters. This technique has been exploited to study the exchange reaction between free actin and the actin–protamine complexes. For these studies the 1:1 actin–protamine complex formed at low ionic strength and the 2:1 actin–protamine complex formed in the presence of 23nm-free Mg2+ have been selected. In the first case the exchange reaction is practically complete in the dead time of the experiment (20s). In the second case, where the complex operates like a true ATPase, the rate of the exchange is initially comparable with the rate of the ATP cleavage. Later on, however, the complex undergoes a change and the rate of the exchange between free actin and the actin bound to protamine becomes lower than the rate of the ATPase reaction. It is proposed that the ATP exchanges for ADP directly on the G-actin bound in the complex.

New multidentate ligands. XXI. Synthesis, proton, and metal ion binding affinities of N,N′,N″-tris[2-(N-hydroxycarbamoyl)ethyl]-1,3,5-benzenetricarboxamide (BAMTPH)

1983 ◽  
Vol 61 (12) ◽  
pp. 2740-2744 ◽  
Author(s):  
Isao Yoshida ◽  
Ichiro Murase ◽  
Ramunas J. Motekaitis ◽  
Arthur E. Martell
Keyword(s):  
Metal Ions ◽  
Metal Ion ◽  
Binding Constants ◽  
Cation Binding ◽  
Ion Binding ◽  
Binding Affinities ◽  
Metal Ion Binding ◽  
Trivalent Metal ◽  
Equilibrium Data ◽  
Trivalent Metal Ions

Synthesis of a new tris-bidentate multidentate ligand, N,N′,N″-tris[2-(N-hydroxycarbamoyl)ethyl]-1,3,5-benzenetricarboxamide (BAMTPH), designed for the binding of trivalent metal ions such as Fe(III), Ga(III), and Al(III), is described. Its cation binding affinities for hydrogen ion and for Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Ga(III), and Al(III) ions are described, and the equilibrium data are compared with those of analogous ligands. The binding constants of trivalent metal ions with the ligand do not show a chelate effect relative to the binding to individual bidentate hydroxamic acids.

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