The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform
Robert P. Hausinger - One of the best experts on this subject based on the ideXlab platform.
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purificatIon characterizatIon and functIonal analysis of a truncated klebsiella aerogenes uree urease accessory protein lacking the histidine rich carboxyl terminus
Journal of Bacteriology, 1996Co-Authors: Timothy G Brayman, Robert P. HausingerAbstract:Klebsiella aerogenes UreE, one of four accessory proteins involved in urease metallocenter assembly, contains a histidine-rich C terminus (10 of the last 15 residues) that is likely to participate in metal Ion coordinatIon by this Nickel-binding protein. To study the functIon of the histidine-rich regIon in urease activatIon, ureE in the urease gene cluster was mutated to result in synthesis of a truncated peptide, H144* UreE, lacking the final 15 residues. Urease activity in cells containing H144* UreE approached the activities for cells possessing the wild-type protein at Nickel Ion concentratIons ranging from 0 to 1 mM in both nutrient-rich and minimal media. In contrast, clear reductIons in urease activities were observed when two ureE deletIon mutant strains were examined, especially at lower Nickel Ion concentratIons. Surprisingly, the H144* UreE, like the wild-type protein, was readily purified with a Nickel-nitrilotriacetic acid resin. Denaturing polyacrylamide gel electrophoretic analysis and N-terminal sequencing confirmed that the protein was a truncated UreE. Size exclusIon chromatography indicated that the H144* UreE peptide associated into a homodimer, as known for the wild-type protein. The truncated protein was shown to cooperatively bind 1.9 +/- 0.2 Ni(II) Ions as assessed by equilibrium dialysis measurements, compared with the 6.05 +/- 0.25 Ni Ions per dimer reported previously for the native protein. These results demonstrate that the histidine-rich motif is not essential to UreE functIon and is not solely responsible for UreE Nickel-binding ability. Rather, we propose that internal Nickel binding sites of UreE participate in urease metallocenter assembly.
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Microbial Nickel Metabolism
Biochemistry of Nickel, 1993Co-Authors: Robert P. HausingerAbstract:As described in Chapters 3–6, four Nickel-dependent enzymes have been isolated and characterized from various microorganisms—urease, hydrogenase, CO dehydrogenase, and methyl coenzyme M reductase. In additIon, specific accessory proteins have been identified as being involved in the functIonal incorporatIon of Nickel Ion into urease and hydrogenase. Intracellular Nickel processing functIons may also be needed for Nickel metallocenter assembly in CO dehydrogenase and for the synthesis of the Nickel-containing coenzyme F430, a component of methyl coenzyme M reductase. These aspects of microbial Nickel metabolism will not be repeated here. Rather, this chapter will focus on Nickel Ion transport into the microbial cell, Nickel Ion toxicity and resistance mechanisms in microbes, and other features related to microbial Nickel metabolism.
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purificatIon and characterizatIon of klebsiella aerogenes uree protein a Nickel binding protein that functIons in urease metallocenter assembly
Protein Science, 1993Co-Authors: Mann Hyung Lee, Stuart H Pankratz, Shengke Wang, Robert A Scott, Michael G Finnegan, Michael K Johnson, Joseph A Ippolito, David W Christianson, Robert P. HausingerAbstract:The Klebsiella aerogenes ureE gene product was previously shown to facilitate assembly of the urease metallocenter (Lee, M.H., et al., 1992, J. Bacteriol. 174, 4324-4330). UreE protein has now been purified and characterized. Although it behaves as a soluble protein, UreE is predicted to possess an amphipathic beta-strand and exhibits unusually tight binding to phenyl-Sepharose resin. Immunogold electron microscopic studies confirm that UreE is a cytoplasmic protein. Each dimeric UreE molecule (M(r) = 35,000) binds 6.05 + 0.25 Nickel Ions (Kd of 9.6 +/- 1.3 microM) with high specificity according to equilibrium dialysis measurements. The Nickel site in UreE was probed by X-ray absorptIon and variable-temperature magnetic circular dichroism spectroscopies. The data are most consistent with the presence of Ni(II) in pseudo-octahedral geometry with 3-5 histidyl imidazole ligands. The remaining ligands are nitrogen or oxygen donors. UreE apoprotein has been crystallized and analyzed by X-ray diffractIon methods. AdditIon of Nickel Ion to apoprotein crystals leads to the development of fractures, consistent with a conformatIonal change upon binding Nickel Ion. We hypothesize that UreE binds intracellular Nickel Ion and functIons as a Nickel donor during metallocenter assembly into the urease apoprotein.
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Animal Nickel Metabolism
Biochemistry of Nickel, 1993Co-Authors: Robert P. HausingerAbstract:All animals, including humans, are constantly exposed to Nickel Ion and particulate Nickel compounds through the food we eat and the air we breath. A small portIon of the ingested Nickel is absorbed by cells lining the small intestine, and additIonal small amounts of Nickel are assimilated by pulmonary cells after inhalatIon. The absorbed Nickel Ion is systemically transported to all tissues by proteinaceous and low-molecular-weight Nickel-binding components in the serum. Although steady-state levels of Nickel are fairly uniform in various tissues of the body, when radiolabeled Nickel Ion is administered to an animal, the metal Ion is rapidly accumulated in the kidney. The kidney and urinary tract serve as the major route of eliminatIon for absorbed Nickel Ion, while nonabsorbed Nickel compounds are eliminated in the feces. Cellular internalizatIon of Nickel Ion can occur by actIon of metal Ion transport proteins, whereas lipophilic Nickel complexes appear capable of diffusIon into cells, and certain cells can phagocytize Nickel particles. Although it remains obscure whether Nickel is an essential or even beneficial trace metal Ion in humans, low concentratIons of Nickel do appear to facilitate optimal growth of several animals. The functIonal roles for Nickel in animals, however, are only poorly understood. In contrast, the toxic, carcinogenic, and other harmful effects of certain Nickel species have been well documented in various systems. This chapter will describe the metabolic flux of Nickel Ion in animals, examine the evidence that Nickel is essential for animal growth, and detail the harmful effects of Nickel compounds on animal cells.
Arnold G Fogg - One of the best experts on this subject based on the ideXlab platform.
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catalytic cathodic stripping voltammetry of oxidized glutathIone at a hanging mercury drop electrode in the presence of Nickel Ion
Talanta, 1995Co-Authors: Florinel G Banica, Arnold G Fogg, Josino Costa MoreiraAbstract:Oxidized glutathIone (GSSG) can be determined after previous accumulatIon on the HMDE at E > −0.2 V (vs. the AgAgCl reference electrode). GSH is formed during the accumulatIon, possibly by a mercury-Ion-assisted hydrolytic disproportIonatIon of GSSG. In the subsequent cathodic scan GSH is released and catalyses the reductIon of Nickel Ion, giving a peak located at −0.6 V. This enables the determinatIon of GSSG by differential-pulse cathodic stripping voltammetry at pH 7.0 in the phosphate acetate or MOPS buffer containing 0.5−1.0 mM Ni(II). The detectIon limit is 10 nM. The calibratIon graph is linear even in the presence of small amounts of human serum albumin, HSA. However, HSA increases the detectIon limit (20 nM for 3 × 10−4% HSA). Acetyl-cysteine in small excess or Cu(II) present as reagent impurity do not interfere. GlutathIone, cysteine and similar compounds, which accumulate as mercury salts and form stable Nickel complexes, will interfere. The method is put forward as a novel alternative stripping voltammetric method to those involving accumulatIon and determinatIon as mercury or copper salts and complexes, in the knowledge that it may have advantages in particular analytical situatIons. In particular the method discriminates against compounds which accumulate as mercury salts but which do not form stable Nickel complexes.
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applicatIon of catalytic stripping voltammetry for the determinatIon of organic sulfur compounds at a hanging mercury drop electrode behaviour of cysteine cystine and n acetylcysteine in the presence of Nickel Ion
Analyst, 1994Co-Authors: Florinel G Banica, Josino Costa Moreira, Arnold G FoggAbstract:The differential-pulse cathodic stripping voltammetry of cysteine (CysH), cystine (Cys) and N-acetylcysteine (Ac-CysH) was studied at a hanging mercury drop electrode at pH 7 in the presence of Nickel Ion, 3-(N-Morpholino)propanesulfonic acid (MOPS) and phosphate–acetate buffer were used as supporting electrolytes. In the presence of CysH, after accumulatIon at potentials ranging between 0.0 and –0.4 V, the catalytic reductIon of Nickel Ion gives a peak at –0.6 V versus the Ag—AgCl reference electrode. An additIonal effect of Nickel Ion is the suppressIon of the cathodic stripping peak due to mercury cysteinate reductIon, thus permitting the simultaneous determinatIon of another thiol with no catalytic activity (e. g., Ac-CysH), Consequently, CysH (or Cys) and Ac-CysH can be determined simultaneously or independently in the same sample. Cys is reduced at potentials preceding the catalytic peak, which is actually due to the CysH thus produced. Some differences between the behaviour of Cys and CysH are due to different accumulatIon mechanisms. The catalytic stripping voltammetry of CysH or Cys exhibits good sensitivity (detectIon limit about 1 nmol dm–3 for 3 min accumulatIon). The stripping voltammetric method described appears to be the first involving adsorptive accumulatIon of a metal complex in which the organic ligand is determined catalytically. Further, this particular method affords some selectivity in the determinatIon of sulfur compounds, which are normally determined by cathodic stripping, voltammetry of their anodically accumulated mercury complexes.
Florinel G Banica - One of the best experts on this subject based on the ideXlab platform.
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catalytic cathodic stripping voltammetry of oxidized glutathIone at a hanging mercury drop electrode in the presence of Nickel Ion
Talanta, 1995Co-Authors: Florinel G Banica, Arnold G Fogg, Josino Costa MoreiraAbstract:Oxidized glutathIone (GSSG) can be determined after previous accumulatIon on the HMDE at E > −0.2 V (vs. the AgAgCl reference electrode). GSH is formed during the accumulatIon, possibly by a mercury-Ion-assisted hydrolytic disproportIonatIon of GSSG. In the subsequent cathodic scan GSH is released and catalyses the reductIon of Nickel Ion, giving a peak located at −0.6 V. This enables the determinatIon of GSSG by differential-pulse cathodic stripping voltammetry at pH 7.0 in the phosphate acetate or MOPS buffer containing 0.5−1.0 mM Ni(II). The detectIon limit is 10 nM. The calibratIon graph is linear even in the presence of small amounts of human serum albumin, HSA. However, HSA increases the detectIon limit (20 nM for 3 × 10−4% HSA). Acetyl-cysteine in small excess or Cu(II) present as reagent impurity do not interfere. GlutathIone, cysteine and similar compounds, which accumulate as mercury salts and form stable Nickel complexes, will interfere. The method is put forward as a novel alternative stripping voltammetric method to those involving accumulatIon and determinatIon as mercury or copper salts and complexes, in the knowledge that it may have advantages in particular analytical situatIons. In particular the method discriminates against compounds which accumulate as mercury salts but which do not form stable Nickel complexes.
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applicatIon of catalytic stripping voltammetry for the determinatIon of organic sulfur compounds at a hanging mercury drop electrode behaviour of cysteine cystine and n acetylcysteine in the presence of Nickel Ion
Analyst, 1994Co-Authors: Florinel G Banica, Josino Costa Moreira, Arnold G FoggAbstract:The differential-pulse cathodic stripping voltammetry of cysteine (CysH), cystine (Cys) and N-acetylcysteine (Ac-CysH) was studied at a hanging mercury drop electrode at pH 7 in the presence of Nickel Ion, 3-(N-Morpholino)propanesulfonic acid (MOPS) and phosphate–acetate buffer were used as supporting electrolytes. In the presence of CysH, after accumulatIon at potentials ranging between 0.0 and –0.4 V, the catalytic reductIon of Nickel Ion gives a peak at –0.6 V versus the Ag—AgCl reference electrode. An additIonal effect of Nickel Ion is the suppressIon of the cathodic stripping peak due to mercury cysteinate reductIon, thus permitting the simultaneous determinatIon of another thiol with no catalytic activity (e. g., Ac-CysH), Consequently, CysH (or Cys) and Ac-CysH can be determined simultaneously or independently in the same sample. Cys is reduced at potentials preceding the catalytic peak, which is actually due to the CysH thus produced. Some differences between the behaviour of Cys and CysH are due to different accumulatIon mechanisms. The catalytic stripping voltammetry of CysH or Cys exhibits good sensitivity (detectIon limit about 1 nmol dm–3 for 3 min accumulatIon). The stripping voltammetric method described appears to be the first involving adsorptive accumulatIon of a metal complex in which the organic ligand is determined catalytically. Further, this particular method affords some selectivity in the determinatIon of sulfur compounds, which are normally determined by cathodic stripping, voltammetry of their anodically accumulated mercury complexes.
Josino Costa Moreira - One of the best experts on this subject based on the ideXlab platform.
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catalytic cathodic stripping voltammetry of oxidized glutathIone at a hanging mercury drop electrode in the presence of Nickel Ion
Talanta, 1995Co-Authors: Florinel G Banica, Arnold G Fogg, Josino Costa MoreiraAbstract:Oxidized glutathIone (GSSG) can be determined after previous accumulatIon on the HMDE at E > −0.2 V (vs. the AgAgCl reference electrode). GSH is formed during the accumulatIon, possibly by a mercury-Ion-assisted hydrolytic disproportIonatIon of GSSG. In the subsequent cathodic scan GSH is released and catalyses the reductIon of Nickel Ion, giving a peak located at −0.6 V. This enables the determinatIon of GSSG by differential-pulse cathodic stripping voltammetry at pH 7.0 in the phosphate acetate or MOPS buffer containing 0.5−1.0 mM Ni(II). The detectIon limit is 10 nM. The calibratIon graph is linear even in the presence of small amounts of human serum albumin, HSA. However, HSA increases the detectIon limit (20 nM for 3 × 10−4% HSA). Acetyl-cysteine in small excess or Cu(II) present as reagent impurity do not interfere. GlutathIone, cysteine and similar compounds, which accumulate as mercury salts and form stable Nickel complexes, will interfere. The method is put forward as a novel alternative stripping voltammetric method to those involving accumulatIon and determinatIon as mercury or copper salts and complexes, in the knowledge that it may have advantages in particular analytical situatIons. In particular the method discriminates against compounds which accumulate as mercury salts but which do not form stable Nickel complexes.
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applicatIon of catalytic stripping voltammetry for the determinatIon of organic sulfur compounds at a hanging mercury drop electrode behaviour of cysteine cystine and n acetylcysteine in the presence of Nickel Ion
Analyst, 1994Co-Authors: Florinel G Banica, Josino Costa Moreira, Arnold G FoggAbstract:The differential-pulse cathodic stripping voltammetry of cysteine (CysH), cystine (Cys) and N-acetylcysteine (Ac-CysH) was studied at a hanging mercury drop electrode at pH 7 in the presence of Nickel Ion, 3-(N-Morpholino)propanesulfonic acid (MOPS) and phosphate–acetate buffer were used as supporting electrolytes. In the presence of CysH, after accumulatIon at potentials ranging between 0.0 and –0.4 V, the catalytic reductIon of Nickel Ion gives a peak at –0.6 V versus the Ag—AgCl reference electrode. An additIonal effect of Nickel Ion is the suppressIon of the cathodic stripping peak due to mercury cysteinate reductIon, thus permitting the simultaneous determinatIon of another thiol with no catalytic activity (e. g., Ac-CysH), Consequently, CysH (or Cys) and Ac-CysH can be determined simultaneously or independently in the same sample. Cys is reduced at potentials preceding the catalytic peak, which is actually due to the CysH thus produced. Some differences between the behaviour of Cys and CysH are due to different accumulatIon mechanisms. The catalytic stripping voltammetry of CysH or Cys exhibits good sensitivity (detectIon limit about 1 nmol dm–3 for 3 min accumulatIon). The stripping voltammetric method described appears to be the first involving adsorptive accumulatIon of a metal complex in which the organic ligand is determined catalytically. Further, this particular method affords some selectivity in the determinatIon of sulfur compounds, which are normally determined by cathodic stripping, voltammetry of their anodically accumulated mercury complexes.
C. Bourauel - One of the best experts on this subject based on the ideXlab platform.
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Nickel Ion release from orthodontic NiTi wires under simulatIon of realistic in-situ conditIons
Journal of Materials Science, 2005Co-Authors: M. Arndt, A. Brück, T. Scully, A. Jäger, C. BourauelAbstract:The increasing use of Nickel containing devices in orthodontics and the growing prevalence of Nickel allergy in the populatIon significantly increases the interest in biocompatibility studies of these devices. The decisive factor determining the biocompatibility of orthodontic wires is their corrosIon behaviour. Therefore seven Nickel titanium levelling arches, one titanium molybdenum, a cobalt chromium and three stainless steel wires were analysed with respect to their corrosIon behaviour under realistic conditIons. Potentiostatic tests to determine rupture potentials in artificial saliva and static immersIon tests in artificial saliva (AS) or lactic acid (LA), as well as immersIon tests with mechanical, thermal and combined mechanical and thermal stresses were performed. Subsequently, the surfaces of the wires were investigated employing scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX) and the Nickel release into the corrosIon media of the specimens was measured with inductively coupled plasma mass spectrometry (ICP-MS). The results yield informatIon not only about the relative corrosIon tendency of the wires under in vitro conditIons but also give a quantitative estimatIon about the Nickel Ion release of the orthodontic wires during in vivo treatment. Generally, the maximum release of Nickel Ions was two orders of magnitude below the daily dietary intake level. Mechanical and thermal loading increases Nickel release in the immersIon tests by a factor of 10 to 30. Two NiTi wires (Dentaurum Tensic, Forestadent Titanol Low Force) examined showed lower rupture potentials and a higher tendency towards corrosIon in the immersIon tests than the others due to their surface compositIon. However these differences are levelled off by long-term mechanical and thermal loading.