Showing papers on "Zinc published in 2006"

Solution-grown zinc oxide nanowires.

Abstract: We review two strategies for growing ZnO nanowires from zinc salts in aqueous and organic solvents. Wire arrays with diameters in the nanoscale regime can be grown in an aqueous solution of zinc nitrate and hexamethylenetetramine. With the addition of poly(ethylenimine), the lengths of the wires have been increased to 25 μm with aspect ratios over 125. Additionally, these arrays were made vertical by nucleating the wires from oriented ZnO nanocrystals. ZnO nanowire bundles have been produced by decomposing zinc acetate in trioctylamine. By the addition of a metal salt to the solution, the ZnO wires can be doped with a range of transition metals. Specifically, ZnO nanowires were homogeneously doped with cobalt and showed a marked deviation from paramagnetic behavior. We conclude by highlighting the use of these solution-grown nanowire arrays in dye-sensitized solar cells. The nanowire cells showed an improvement in the charge collection efficiency over traditional nanoparticle cells.

Zinc oxide nanocomb biosensor for glucose detection

Abstract: Single crystal zinc oxide nanocombs were synthesized in bulk quantity by vapor phase transport. A glucose biosensor was constructed using these nanocombs as supporting materials for glucose oxidase (GOx) loading. The zinc oxide nanocomb glucose biosensor showed a high sensitivity (15.33μA∕cm2mM) for glucose detection and high affinity of GOx to glucose (the apparent Michaelis-Menten constant KMapp=2.19mM). The detection limit measured was 0.02mM. These results demonstrate that zinc oxide nanostructures have potential applications in biosensors.

A Fungal Family of Transcriptional Regulators: the Zinc Cluster Proteins

Abstract: The trace element zinc is required for proper functioning of a large number of proteins, including various enzymes. However, most zinc-containing proteins are transcription factors capable of binding DNA and are named zinc finger proteins. They form one of the largest families of transcriptional regulators and are categorized into various classes according to zinc-binding motifs. This review focuses on one class of zinc finger proteins called zinc cluster (or binuclear) proteins. Members of this family are exclusively fungal and possess the well-conserved motif CysX2CysX6CysX5-12CysX2CysX6-8Cys. The cysteine residues bind to two zinc atoms, which coordinate folding of the domain involved in DNA recognition. The first- and best-studied zinc cluster protein is Gal4p, a transcriptional activator of genes involved in the catabolism of galactose in the budding yeast Saccharomyces cerevisiae. Since the discovery of Gal4p, many other zinc cluster proteins have been characterized; they function in a wide range of processes, including primary and secondary metabolism and meiosis. Other roles include regulation of genes involved in the stress response as well as pleiotropic drug resistance, as demonstrated in budding yeast and in human fungal pathogens. With the number of characterized zinc cluster proteins growing rapidly, it is becoming more and more apparent that they are important regulators of fungal physiology.

Large Expression Differences in Genes for Iron and Zinc Homeostasis, Stress Response, and Lignin Biosynthesis Distinguish Roots of Arabidopsis thaliana and the Related Metal Hyperaccumulator Thlaspi caerulescens

Abstract: The micronutrient zinc has an essential role in physiological and metabolic processes in plants as a cofactor or structural element in 300 catalytic and noncatalytic proteins, but it is very toxic when available in elevated amounts. Plants tightly regulate their internal zinc concentrations in a process called zinc homeostasis. The exceptional zinc hyperaccumulator species Thlaspi caerulescens can accumulate up to 3% of zinc, but also high amounts of nickel and cadmium, without any sign of toxicity. This should have drastic effects on the zinc homeostasis mechanism. We examined in detail the transcription profiles of roots of Arabidopsis thaliana and T. caerulescens plants grown under deficient, sufficient, and excess supply of zinc. A total of 608 zinc-responsive genes with at least a 3-fold difference in expression level were detected in A. thaliana and 352 in T. caerulescens in response to changes in zinc supply. Only 14% of these genes were also zinc responsive in A. thaliana. When comparing A. thaliana with T. caerulescens at each zinc exposure, more than 2,200 genes were significantly differentially expressed (>or=5-fold and false discovery rate < 0.05). While a large fraction of these genes are of yet unknown function, many genes with a different expression between A. thaliana and T. caerulescens appear to function in metal homeostasis, in abiotic stress response, and in lignin biosynthesis. The high expression of lignin biosynthesis genes corresponds to the deposition of lignin in the endodermis, of which there are two layers in T. caerulescens roots and only one in A. thaliana.

Zip14 (Slc39a14) mediates non-transferrin-bound iron uptake into cells

Abstract: Zip14 is a member of the SLC39A zinc transporter family, which is involved in zinc uptake by cells. Up-regulation of Zip14 by IL-6 appears to contribute to the hepatic zinc accumulation and hypozincemia of inflammation. At least three members of the SLC39A family transport other trace elements, such as iron and manganese, in addition to zinc. We analyzed the capability of Zip14 to mediate non-transferrin-bound iron (NTBI) uptake by overexpressing mouse Zip14 in HEK 293H cells and Sf9 insect cells. Zip14 was found to localize to the plasma membrane, and its overexpression increased the uptake of both 65Zn and 59Fe. Addition of bathophenanthroline sulfonate, a cell-impermeant ferrous iron chelator, inhibited Zip14-mediated iron uptake from ferric citrate, suggesting that iron is taken up by HEK cells as Fe2+. Iron uptake by HEK and Sf9 cells expressing Zip14 was inhibited by zinc. Suppression of endogenous Zip14 expression by using Zip14 siRNA reduced the uptake of both iron and zinc by AML12 mouse hepatocytes. Zip14 siRNA treatment also decreased metallothionein mRNA levels, suggesting that compensatory mechanisms were not sufficient to restore intracellular zinc. Collectively, these results indicate that Zip14 can mediate the uptake of zinc and NTBI into cells and that it may play a role in zinc and iron metabolism in hepatocytes, where this transporter is abundantly expressed. Because NTBI is commonly found in plasma of patients with hemochromatosis and transfusional iron overload, Zip14-mediated NTBI uptake may contribute to the hepatic iron loading that characterizes these diseases.

Functional finishing of cotton fabrics using zinc oxide–soluble starch nanocomposites

Abstract: Zinc oxide–soluble starch nanocomposites (nano-ZnO) synthesized using water as a solvent and soluble starch as a stabilizer is impregnated onto cotton fabrics to impart antibacterial and UV-protection functions. Nano-ZnO synthesized by reacting zinc nitrate with sodium hydroxide in the presence of soluble starch absorbed strongly at 361 nm due to the quantum confinement effect. The average size of ZnO nanoparticles is estimated to be 38 ± 3 nm using a transmission electron microscope (TEM); this was confirmed by x-ray diffraction analysis and the effective mass approximation method. The starch content in synthesized nano-ZnO was estimated to be 37.57% using thermo-gravimetric analysis. The nano-ZnO impregnated cotton fabrics showed excellent antibacterial activity against two representative bacteria, Staphylococcus aureus (Gram positive) and Klebsiella pneumoniae (Gram negative). Also, nano-ZnO impregnation enhanced the protection of cotton fabrics against UV radiation in comparison with the untreated cotton fabrics.

Zinc-buffering capacity of a eukaryotic cell at physiological pZn.

Abstract: In spite of the paramount importance of zinc in biology, dynamic aspects of cellular zinc metabolism remain poorly defined at the molecular level. Investigations with human colon cancer (HT-29) cells establish a total cellular zinc concentration of 264 microM. Remarkably, about 10% of the potential high-affinity zinc-binding sites are not occupied by zinc, resulting in a surplus of 28 muM ligands (average Kd(c) = 83 pM) that ascertain cellular zinc-buffering capacity and maintain the "free" zinc concentration in proliferating cells at picomolar levels (784 pM, pZn = 9.1). This zinc-buffering capacity allows zinc to fluctuate only with relatively small amplitudes (DeltapZn = 0.3; below 1 nM) without significantly perturbing physiological pZn. Thus, the "free" zinc concentrations in resting and differentiated HT-29 cells are 614 pM and 1.25 nM, respectively. The calculation of these "free" zinc concentrations is based on measurements at different concentrations of the fluorogenic zinc-chelating agent and extrapolation to a zero concentration of the agent. It depends on the state of the cell, its buffering capacity, and the zinc dissociation constant of the chelating agent. Zinc induction of thionein (apometallothionein) ensures a surplus of unbound ligands, increases zinc-buffering capacity and the availability of zinc (DeltapZn = 0.8), but preserves the zinc-buffering capacity of the unoccupied high-affinity zinc-binding sites, perhaps for crucial physiological functions. Jointly, metallothionein and thionein function as the major zinc buffer under conditions of increased cellular zinc.

In vivo expression and functional characterization of the zinc transporter ZnT8 in glucose-induced insulin secretion

Abstract: Insulin-secreting pancreatic beta cells are exceptionally rich in zinc. In these cells, zinc is required for zinc-insulin crystallization within secretory vesicles. Secreted zinc has also been proposed to be a paracrine and autocrine modulator of glucagon and insulin secretion in pancreatic alpha and beta cells, respectively. However, little is known about the molecular mechanisms underlying zinc accumulation in insulin-containing vesicles. We previously identified a pancreas-specific zinc transporter, ZnT-8, which colocalized with insulin in cultured beta cells. In this paper we studied its localization in human pancreatic islet cells, and its effect on cellular zinc content and insulin secretion. In human pancreatic islet cells, ZnT-8 was exclusively expressed in insulin-producing beta cells, and colocalized with insulin in these cells. ZnT-8 overexpression stimulated zinc accumulation and increased total intracellular zinc in insulin-secreting INS-1E cells. Furthermore, ZnT-8-overexpressing cells display enhanced glucose-stimulated insulin secretion compared with control cells, only for a high glucose challenge, i.e. >10 mM glucose. Altogether, these data strongly suggest that the zinc transporter ZnT-8 is a key protein for both zinc accumulation and regulation of insulin secretion in pancreatic beta cells.

Toll-like receptor-mediated regulation of zinc homeostasis influences dendritic cell function.

Abstract: Zinc is a trace element that is essential for the function of many enzymes and transcription factors. Zinc deficiency results in defects in innate and acquired immune responses. However, little is known about the mechanism(s) by which zinc affects immune cell function. Here we show that stimulation with the Toll-like receptor 4 agonist lipopolysaccharide (LPS) altered the expression of zinc transporters in dendritic cells and thereby decreased intracellular free zinc. A zinc chelator mimicked the effects of LPS, whereas zinc supplementation or overexpression of the gene encoding Zip6, a zinc transporter whose expression was reduced by LPS, inhibited LPS-induced upregulation of major histocompatibility complex class II and costimulatory molecules. These results establish a link between Toll-like receptor signaling and zinc homeostasis.

Modified zinc oxide thick film resistors as NH3 gas sensor

Abstract: Screen printed thick films of pure and RuO 2 -doped zinc oxide were prepared. Pure zinc oxide films were also surface modified with ruthenium chloride. Gas sensing properties of the pure, doped and surface modified films were studied. The films were observed to be most sensitive to NH 3 gas. The results are discussed and interpreted.

Zinc coordination environments in proteins as redox sensors and signal transducers.

Abstract: Zinc/cysteine coordination environments in proteins are redox-active. Oxidation of the sulfur ligands mobilizes zinc, while reduction of the oxidized ligands enhances zinc binding, providing redox control over the availability of zinc ions. Some zinc proteins are redox sensors, in which zinc release is coupled to conformational changes that control varied functions such as enzymatic activity, binding interactions, and molecular chaperone activity. Whereas the released zinc ion in redox sensors has no known function, the redox signal is transduced to specific and sensitive zinc signals in redox transducers. Released zinc can bind to sites on other proteins and modulate signal transduction, generation of metabolic energy, mitochondrial function, and gene expression. The paradigm of such redox transducers is the zinc protein metallothionein, which, together with its apoprotein, thionein, functions at a central node in cellular signaling by redistributing cellular zinc, presiding over the availability of zinc, and interconverting redox and zinc signals. In this regard, the transduction of nitric oxide (NO) signals into zinc signals by metallothionein has received particular attention. It appears that redox-inert zinc has been chosen to control some aspects of cellular thiol/disulfide redox metabolism. Tight control of zinc is essential for redox homeostasis because both increases and decreases of cellular zinc elicit oxidative stress. Depending on its availability, zinc can be cytoprotective as a pro-antioxidant or cytotoxic as a pro-oxidant. Any condition with acute or chronic oxidative stress is expected to perturb zinc homeostasis.

Measuring Picomolar Intracellular Exchangeable Zinc in PC-12 Cells Using a Ratiometric Fluorescence Biosensor

Abstract: Zinc plays both physiological and pathological roles in biology, making it of increasing interest. To date, intracellular free zinc has been measured in cell types supplemented with or enriched in zinc, such as hippocampal neurons. Here we quantitatively image intracellular exchangeable zinc in an ordinary resting cell culture line (PC-12), using an excitation ratiometric fluorescent biosensor based on carbonic anhydrase (CA). Human CA II has a Kd of 4 pM for zinc and suffers no interference from millimolar calcium or magnesium ions. The CA-based biosensor was readily introduced into the cell by a novel approach: fusing a transactivator of transcription (TAT)-derived cell penetrating peptide to the CA molecule and adding it to the cells. Our results indicate that the resting concentration is approximately 5–10 pM in cytoplasm and nucleus. Interestingly, the tetrakis(2-pyridylmethyl)ethylenediamine (TPEN)–Zn complex and TPEN are both apoptogenic for this cell line.