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At least 235 records · Page 13Linked to original sources
PubMed1997

A new metal-binding site for yeast phosphoglycerate kinase as determined by the use of a metal-ATP analog.

Suicide substrate beta, gamma-bidentate Rh(III)ATP (RhATP) was used to map the metal ion-binding site in yeast phosphoglycerate kinase (PGK). Cleavage of the RhATP-inactivated enzyme with pepsin and subsequent separation of peptides by reverse-phase high-performance liquid chromatography gave two Rh-nucleotide bound peptides. One of the peptides corresponded to the C-terminal residues of PGK, and the other to a part of helix V. Of the four glutamates present in the C-terminal peptide, Glu 398 may be a likely metal coordination site. Therefore, importance of the C-terminal residues in PGK catalysis may be attributed, in part to the coordination of metal ion of the metal-ATP substrate. Metal coordination may then align the C-terminal peptide to extend toward the N-terminal domain and form the "closed" active site. Results presented in this paper suggest that one or more side chains of the enzyme may be coordinated to the metal ion in the PGK.3-phospho-D-glycerate-RhATP complex, and that exchange-inert metal-ATP analogs could be used to determine metal coordination sites on kinases and other metal-ATP-utilizing enzymes.

Adenosine Triphosphate↗
PubMed1990

Differential interaction of peptides and protein surface structures with free metal ions and surface-immobilized metal ions.

We have examined the influence of free metal ions on the affinity of structurally-defined proteins and peptides for model surface-immobilized metal ions. The model proteins chosen differed widely in both the type and quantity of surface-accessible electron donor groups. Metal ion affinity chromatography and equilibrium binding analyses demonstrated that the presence of excess free Cu(II) ions did not measurably affect either the affinity or the binding capacity of lysozyme for immobilized iminodiacetate-Cu(II). Similarly, the presence of excess free Cu(II) ions did not detectably affect the chromatographic behavior or measured affinity of either copper-saturated lactoferrin or iron-saturated lactoferrin for the immobilized Cu(II) ions. Its binding capacity however, was diminished. The affinities of small peptides for immobilized Cu(II) ions was found to be related to their number of His residues. Peptides with 0, 1, 2 and 3 His residues were resolved by high-performance immobilized Cu(II) affinity chromatography in both the presence and absence of added Cu(II) ions. In the presence of excess free Cu(II) ions, however, retention (affinities) of these peptides by immobilized Cu(II) ions was increased in relation to their number of His residues. These data demonstrate that protein surface binding sites for free and immobilized metal ions are functionally distinct. The presence of free and/or protein surface-bound metal ions does not preclude interaction with the same immobilized metal ions. Stationary phase immobilized metal ions can be a useful model system through which we can better understand the influence of macromolecular surface-immobilized metal ions on macromolecular recognition events. The significance of these findings are also important to the design of other site-specific and domain-specific affinity reagents involving metal ions.

Apoproteins↗
PubMed1991

Induction of several acute-phase protein genes by heavy metals: a new class of metal-responsive genes.

Acute-phase reactants, metallothioneins, and heat-shock proteins are the products of three families of genes that respond to glucocorticoids and cytokines. Metallothioneins and heat-shock proteins, however, are also stimulated by heavy metals, whereas very little is known about the effect of heavy metals on acute-phase-reactant genes. We have studied the effect of heavy metals (Hg, Cd, Pb, Cu, Ni, and Zn) and Mg on the acute-phase reactants alpha 1-acid glycoprotein, C-reactive protein, alpha 1-antitrypsin and alpha 1-antichymotrypsin. alpha 1-Acid glycoprotein and C-reactive protein mRNA levels were increased severalfold in livers of heavy-metal-treated Balb/c mice. The strongest induction was mediated by Hg, followed in order of response by Cd greater than Pb greater than Cu greater than Ni greater than Zn greater than Mg. None of the metals affected the mRNA levels of albumin, alpha 1-antitrypsin, and alpha 1-antichymotrypsin. Furthermore, failure to repress albumin, a negative acute-phase reactant, indicated that the induction of these genes was not due to a metal-mediated inflammatory response. The metals also induced alpha 1-acid glycoprotein and C-reactive protein in adrenalectomized animals, indicating that induction by the heavy metals is not mediated by the glucocorticoid induction pathway. Sequence analysis has revealed a region of homology to metal-responsive elements in the alpha 1-acid glycoprotein and C-reactive protein promoters. Additionally, an alpha 1-acid glycoprotein expression vector, pAGP(-595)CAT, responded to Hg and Cd when transfected into human HepG2 cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute-Phase Proteins↗
PubMed2002

Brain-specific metallothionein-3 has higher metal-binding capacity than ubiquitous metallothioneins and binds metals noncooperatively.

Zinc metabolism in the cells is largely regulated by ubiquitous small proteins, metallothioneins (MT). Metallothionein-3 is specifically expressed in the brain and is down regulated in Alzheimer's disease. We demonstrate by mass spectrometry that MT-3, in contrast to common MTs, binds Zn(2+) and Cd(2+) in a noncooperative manner and can also bind higher stoichiometries of metals than seven. MT-3 reconstituted with seven metals exists in a dynamic equilibrium of different metalloforms, where the prevalent metalloform is Me(7)MT-3, but metalloforms with 6, 8, and even 9 metals are also present. The results from pH and stability studies demonstrate that the heterogeneity of metalloforms originates from the N-terminal beta-cluster, whereas the C-terminal alpha-cluster of MT-3 binds four metal ions such as that of common MTs. Experiments with EDTA demonstrate that the beta-cluster of ZnMT-3 has a higher metal transfer potential than the beta-cluster of Zn(7)MT-2. Moreover, ZnMT-3 loses metals during ultrafiltration. MT-3, reconstituted with an excess of Zn(2+) or Cd(2+), exists as a dynamic mixture of metalloforms with higher than 7 metal stoichiometries (8-11). Such forms of ZnMT-3 are unstable and decompose partly already during a rapid gel filtration, whereas CdMT-3 forms are more stable. Extra metal ions may bind to the beta-cluster region as well as to the carboxylates of MT-3. The specific metal-binding properties of MT-3 could be functionally implemented for buffering of fluctuating concentrations of zinc in zincergic neurons and for transfer of zinc to synaptic vesicles.

Alzheimer Disease↗
PubMed2000

Influence of metal surface finishing on porcelain porosity and beam failure loads at the metal-ceramic interface.

STATEMENT OF THE PROBLEM: Investigators suggest that metals should be finished in 1 direction before porcelain application to minimize metal irregularities and trapped contaminants. These irregularities are thought to be focal points for porosity and crack propagation. PURPOSE: This study investigated the influence of metal finishing and sandblasting on (1) porosity production at the porcelain-metal interface, and (2) porcelain-metal beam failure load. MATERIAL AND METHODS: Eighty cast metal samples were divided into 4 test groups: (A) bidirectional finish/sandblasting; (B) unidirectional finish/sandblasting (C) bidirectional finish only; and (D) unidirectional finish only. The porcelain applied was 1.5 mm thick. Samples were sectioned longitudinally. Half of the samples were subjected to a 3-point flexural test. The remaining samples were sectioned into 4 slices and were examined with a light microscope (x500). Number and diameter of porosities at the metal-porcelain interface were recorded. RESULTS: Mean loads at failure (lbs) were as follows: A, 11.1 +/- 1.3 (5.03 +/- 0.58 Kg); B, 11.2 +/- 1.7 (5. 08 +/- 0.77 Kg); C, 4.0 +/- 1.8 (1.81 +/- 0.81 Kg); and D, 5.0 +/- 2. 1 (2.26 +/- 0.95 Kg). Groups A and B were significantly different from groups C and D (P<.0001). Nonsandblasted samples (C and D) exhibited a separation at the ceramometal interface, which prevented quantification of porosity size and number. Average interface porosity sizes (microm) (A, 8.99 +/- 1.92; B, 10.03 +/- 1.86) showed no significant difference. The mean interface porosity number (A, 62. 3 +/- 16.02; B, 67.4 +/- 10.01) showed no significant difference. CONCLUSION: Direction of metal finishing did not affect the porosity number and size at the ceramometal interface or the beam failure loads. Sandblasting increased the beam failure loads. Nonsandblasted samples showed detachment of the porcelain from the metal.

Aluminum Oxide↗
PubMed2005

Comparison of bond strength of a pressed ceramic fused to metal versus feldspathic porcelain fused to metal.

PURPOSE: To compare the debonding/crack initiation strength (D/CIS) of a low-fusing pressable leucite-based glass ceramic (PC) fused to metal to a feldspathic porcelain (FP) fused to metal. MATERIALS & METHODS: As per ISO 9693:1999, 40 rectangular metal specimens (25.0 mm x 0.5 mm x 3.0 mm) were prepared. Twenty of the specimens were cast in a base metal nickel-chromium alloy (BA), and 20 were cast in a noble metal palladium-silver alloy (NA). Ten randomly selected NA and BA alloy specimens had FP applied. The remaining 10 NA and BA alloy specimens had ash-free wax patterns applied, the metal-wax complexes invested, and were pressed with a PC. The dimensions of the ceramic specimens were 8.0 mm x 1.0 mm x 3.0 mm, creating a combined metal-ceramic complex thickness of 1.5 mm. All specimens were subject to a three-point bending test at a crosshead speed of 1.5 mm/min. Fracture loads were recorded in Newtons and D/CISs calculated by the formula tau(b)=k x F(fail). RESULTS: Mean D/CISs, measured in MPa (standard deviations): NA-FP 32.56 (4.62), NA-PC 30.23 (5.06), BA-FP 30.98 (4.41), and BA-PC 31.81 (3.48). A two-way ANOVA (p > 0.05) did not demonstrate significant difference between groups. CONCLUSION: The debonding/crack initiation strength of a low-fusing pressable leucite-based glass ceramic fused to metal was equivalent to that of a feldspathic porcelain fused to metal.

Aluminum Silicates↗
PubMed2006

Bacterial tolerances to metals and antibiotics in metal-contaminated and reference streams.

Anthropogenic-derived sources of selection are typically implicated as mechanisms for maintaining antibiotic resistance in the environment. Here we report an additional mechanism for maintaining antibiotic resistance in the environment through bacterial exposure to metals. Using a culture-independent approach, bacteria sampled along a gradient of metal contamination were more tolerant of antibiotics and metals compared to bacteria from a reference site. This evidence supports the hypothesis that metal contamination directly selects for metal tolerant bacteria while co-selecting for antibiotic tolerant bacteria. Additionally, to assess how antibiotic and metal tolerance may be transported through a stream network, we studied antibiotic and metal tolerance patterns over three months in bacteria collected from multiple stream microhabitats including the water column, biofilm, sediment and Corbicula fluminea (Asiatic clam) digestive tracts. Sediment bacteria were the most tolerant to antibiotics and metals, while bacteria from Corbicula were the least tolerant. Differences between microhabitats may be important for identifying reservoirs of resistance and for predicting how these genes are transferred and transported in metal-contaminated streams. Temporal dynamics were not directly correlated to a suite of physicochemical parameters, suggesting that tolerance patterns within microhabitats are linked to a complex interaction of the physicochemical characteristics of the stream.

Animals↗
PubMed2001

Impact of metal pools and soil properties on metal accumulation in Folsomia candida (Collembola).

Soil-dwelling organisms are exposed to metals in different ways. Evidence exists for predominant pore water uptake of metals by soft-bodied oligochaete species. In the present research, uptake kinetics of metals and the metalloid As by the semi-soft-bodied springtail Folsomia candida were studied, for which uptake via the pore water is less obvious. Springtails were exposed in 16 field soils and in metal-spiked artificial Organization for Economic Cooperation and Development (Paris, France) soil (OECD soil). Subsequently, accumulation parameters were statistically related to soil metal pools and soil properties. In Cd-spiked OECD soil, internal Cd levels were linearly related to external Cd concentrations, whereas the springtails maintained fixed internal levels of Cu and Zn regardless of spiked concentrations. In the field soils, all body concentrations of the elements As, Cr, and Ni were below detection limit. The essential metals Cu and Zn were presumably regulated, and no influence of soil characteristics could be demonstrated. For Cd and Pb, accumulation patterns were correlated mainly to solid-phase soil characteristics. The presence of these explanatory variables in the multiple correlations suggests that an uptake mechanism that is solely determined by pore water concentrations should not be taken as a universally applicable principle in risk assessments of metals for soil invertebrates. Cadmium in OECD soils was more available for uptake than in the field soils. The difference remained when extractability was taken into account. The results suggest that experiments in OECD soil cannot be used directly in risk assessment for nonessential metals (at least for F. candida), although a reduction of uncertainties in metal risk assessment can be reached by consistent use of body residues rather than external concentrations.

Animals↗
PubMed2000

Use of a commercially available metal detector for the localization of metallic foreign body ingestion in children.

UNLABELLED: Metallic foreign body (FB) ingestion is a common occurrence in the general paediatric population. We have shown that the use of a commercially available metal detector is sensitive in localizing and confirming metallic FB objects in the digestive tract. METHOD: In a double-blinded randomized control trial, we used a commercially available metal detector to localize metal coins in the digestive tract in an animal model. Localization of the coins was confirmed using fluoroscopy. In 10 consecutive patients with metallic FB ingestion, detection and localization of the FB using the metal detector was compared with standard confirmatory radiographic imaging. RESULTS: Using a commercially available, hand-held metal detector, we were able to localize a metallic FB in the gastrointestinal tract with 100% sensitivity in both the animal model and in 10 paediatric patients.

Child↗
PubMed1983

[In vitro dissolution of metallic oxides in human plasma and binding of metals to plasma proteins--effect of chelators].

The solubility in biological liquids of oxides is one of the factors which determinate the speed of penetration into the blood stream of toxic agents contained in solid particles inside pulmonary alveoli. This solubility was studied in vitro for the six following metal oxides: Cd, Cr, Fe, Mn, Pb, Zn, by holding particle oxides in suspension into human plasma at 37 degrees C, during variable time. The experimentation was realized on particles which belong to two categories which sizes are 0.45-2 and 2-5 mu. The evolution of metal oxide dissolved level according to time have enabled exponential relation parameters to be calculated. These parameters translate the particle oxide dissolution into plasma and have permitted to classify metal oxide in decreasing solubility order: Cd, Zn, PbO, Fe2O3, Fe3O4, Mn, PbO2, Pb3O4 and Cr2O3. The second part of the experimentation is about dissolved metal distribution between the different protein fractions. Dissolved metal is distributed between diffusible metal (lower than 10 per cent) and metal binding proteins chiefly in albumin except for Fe which is bound to transferrin. Chelating agents into plasma reduce the proportion of metals bound to proteins. EDTA Ca is energetic on all metals mainly on Lead, Cadmium, and Zinc. N-acetyl-DL penicillamin is less energetic. Meso 2,3 dimercapto succinic acid, and 2,3 dimercapto-1-propan sulfonic acid have an effect only on Lead but in a very light way. Desferrioxamin release a great proportion of Iron bound to proteins. These results, obtained in vitro, are similar to those from animal experimentation or those observed in human therapeutic.

Blood Proteins↗
PubMed2000

Effect of alkali metal cationization and multiple alkali metal exchange on the collision-induced dissociation of loganic acid studied by electrospray ionization tandem mass spectrometry

Under electrospray ionization conditions loganic acid undergoes alkali metal (Li, Na and K) exchange and alkali metal cationization. Multiple exchanges of up to four alkali metal ions are observed. Different populations of metal exchanged species are produced during electrospray ionization. Collision-induced dissociation of ammonium cationized species is compared with that of metal cationized species to study the effect of metal cationization. Glycosidic cleavage and ring cleavages of aglycone and sugar moieties are the major fragmentation pathways observed during collision-induced dissociation. The fragmentations of the highly metal exchanged species indicate the opening of the pyran ring. Collision-induced dissociation of the various metal exchanged and metal cationized species also reveals the nature of the different populations. Copyright 2000 John Wiley & Sons, Ltd.

Journal Article↗
PubMed2000

Novel metal-to-metal silyl-migration reactions in heterometallic complexes.

An unprecedented, intramolecular metal-to-metal silyl ligand migration reaction has been discovered in a series of phosphido-bridged iron-platinum complexes and which may be triggered by an external nucleophile. Thus, reaction of solutions of [(OC)3-(R1/3Si)Fe(mu-PR2R3)Pt(1,5-COD) (1a R1 = OMe, R2 = 3 = Ph; 1b R1 = OMe, R2 = R3 = Cy; 1c R1 = Ph, R2 = R3 = Ph; 1d R1 = Ph, R2 = R3 = Cy; 1e R1 = Ph, R1 = H, R3 = Ph) in CH2Cl2 with CO rapidly afforded the corresponding complexes [(OC)4Fe(mu-PR2R3)Pt(SiR1/3)-(CO)] (2a-e) in which the silyl ligand has migrated from Fe to Pt, while two CO ligands have been ligated, one on each metal. When 1a or 1c was slowly treated with two equivalents of tBuNC at low temperature, quantitative displacement of the COD ligand was accompagnied by silyl migration from Fe to Pt and coordination of an isonitrile ligand to Fe and to Pt to give [(OC)3-(tBuNC)Fe(mu-PPh2)Pt[Si(OMe)3](CNtBu)] (3a) and [(OC)3(tBuNC)-Fe(mu-PPh2)Pt[SiPh3](CNtBu)] (3c). Reaction of 2a with one equivalent of tBuNC selectively led to substitution of the Pt-bound CO to give [(OC)4-Fe(mu-PCy2)Pt[Si(OMe)3](CNtBu)] (4b), which reacted with a second equivalent of tBuNC to give [(OC)4Fe(mu-PCy2)-Pt[Si(OMe)3](CNtBu)2] (5b) in which the metal-metal bond has been cleaved. Opening of the Fe-Pt bond was also observed upon reaction of 3a with tBuNC to give [(OC)3(tBuNC)-Fe(mu-PPh2)Pt[Si(OMe)3](CNtBu)2] (6). The silyl ligand migrates from Fe, in which it is trans to mu-PR2R3 in all the metal-metal-bonded complexes, to a position cis to the phosphido bridge on Pt. However, in 5a,b and 6 with no metal-metal bond, the Pt-bound silyl ligand is trans to the phosphido bridge. The intramolecular nature of the silyl migration, which may be formally viewed as a redox reaction, was established by a cross-over experiment consisting of the reaction of 1a and 1d with CO; this yielded exclusively 2a and 2d. The course of the silyl-migration reaction was found to depend a) on the steric properties of the -SiR1/3 ligand, and for a given mu-PR2R3 bridge (R2 = R3 = Ph), the migration rate decreases in the sequence Si(OMe)3> SiMe2Ph> SiMePh2>>SiPh3; b) on the phosphido bridge and for a given silyl ligand (R1 = OMe), the migration rate decreases in the order mu-PPh2 >> mu-PHCy; c) on the external nucleophile since reaction of 1c with two equivalents of P(OMe)3, P(OPh)3 or Ph2PCH2C(O)Ph led solely to displacement of the COD ligand with formation of 11a-c, respectively, whereas reaction with two equivalents of tBuNC gave the product of silyl migration 3c. Reaction of [(OC)3-[(MeO)3Si]Fe(mu-PPh2)Pt(PPh3)2] (7a) with tBuNC (even in slight excess) occurred stereoselectively with replacement of the PPh3 ligand trans to mu-PPh2, whereas reaction with CO led first to [(OC)3((MeO)3Si)Fe(mu-PPh2)Pt(CO)-(PPh3)] (8a), which then isomerized to the migration product [(OC)4Fe(mu-PPh2)Pt[Si(OMe)3](PPh3)] (9a). Most complexes were characterized by elemental analysis, IR and 1H, 31P, 13C, and 29Si NMR spectroscopy, and in five cases by X-ray diffraction.

Journal Article↗
PubMed2000

Metal Ion Catalysis in the Hydrolysis of Esters of 2-Hydroxy-1,10-phenanthroline: The Effects of Metal Ions on Intramolecular Carboxyl Group Participation.

Rate constants have been determined for hydrolysis of the acetate, glutarate, and phthalate monoesters of 2-hydroxy-1,10-phenanthroline in water at 30 degrees C and &mgr; = 0.1 M with KCl. The hydrolysis reactions of the esters are hydroxide ion catalyzed at pH > 9. The phthalate and glutarate monoesters have in addition pH-independent reactions from pH 5.5 to 9 that involve intramolecular participation by the neighboring carboxylate anion. The pH-independent reaction of the glutarate monoester is approximately 5-fold faster than that of the phthalate monoester. The plots of log k(obsd) vs pH for hydrolysis of the carboxyl substituted esters are bell shaped at pH < 5, which indicates a rapid reaction of the zwitterionic species (carboxyl anion and protonated phenanthroline nitrogen). The divalent metal ions, Cu(2+), Ni(2+), Zn(2+), and Co(2+), complex strongly with the esters; saturation occurs at metal ion concentrations less than 0.01 M. The 1:1 metal ion complexes have greatly enhanced rates of hydrolysis; the second-order rate constants for the OH(-) reactions are increased by factors of 10(5) to 10(8) by the metal ion. The pH-rate constant profiles for the phthalate and glutarate ester metal ion complexes have a sigmoidal region below pH 6 that can be attributed to a metal ion-promoted carboxylate anion nucleophilic reaction. The carboxyl group reactions are enhanced 10(2) - to 10(3) -fold by the metal ions, which allows the neighboring group reaction to be competitive with the favorable metal ion-promoted OH(-) reaction at pH < 6, but not at pH > 6. The half-lives of the pH-independent neighboring carboxyl group reactions of the Cu(II) complexes at 30 degrees C are approximately l2 s. The other metal ion complexes are only slightly less reactive (half-lives vary from 2.5 to 40 s). These are the most rapid neighboring carboxyl group reactions that have been observed in ester hydrolysis. Copyright 2000 Academic Press.

Journal Article↗
PubMed2007

Metal ion binding properties of Triticum [corrected] aestivum Ec-1 metallothionein: evidence supporting two separate metal thiolate clusters.

Metallothioneins are ubiquitous low molecular mass, cysteine-rich proteins with an extraordinary high metal ion content. In contrast to the situation for the vertebrate forms, information regarding the properties of members of the plant metallothionein family is still scarce. We present the first spectroscopic investigation aiming to elucidate the metal ion binding properties and metal thiolate cluster formation of the Triticum [corrected] aestivum (common wheat) early cysteine-labeled plant metallothionein (Ec-1). For this, the protein was overexpressed recombinantly in Escherichia coli. Recombinant Ec-1 is able to bind a total of six divalent d10 metal ions in a metal thiolate cluster arrangement. The pH stability of the zinc and cadmium clusters investigated is comparable to stabilities found for mammalian metallothioneins. Using cobalt(II) as a paramagnetic probe, we were able to show the onset of cluster formation taking place with the addition of a fourth metal ion equivalent to the apo protein. Limited proteolytic digestion experiments complemented with mass spectrometry and amino acid analysis provide clear evidence for the presence of two separate metal thiolate clusters. One cluster consists of four metal ions and is made up by a part of the protein containing 11 cysteine residues, comparable to the situation found in the mammalian counterparts. The second cluster features two metal ions coordinated by six cysteine residues. The occurrence of the latter cluster is unprecedented in the metallothionein superfamily so far.

Amino Acid Sequence↗