Zinc sequestration

Stein, O.R., Borden-Stewart, D.J., Hook, P.B., and Jones, W.L., Seasonal influence on sulfate reduction and zinc sequestration in subsurface treatment wetlands, Water Research, 41 (15), 3440-3448, 2007. 

As we saw in Chapter 7, there are several plasma membrane zinc uptake transporters in yeast. Within the cell, a number of other proteins are involved in zinc transport within the cell. S. cerevisiae is unusual in that it does not appear to have any plasma membrane zinc efflux transporters. This is to a large extent compensated by the capacity of the vacuole to serve as a major site of zinc sequestration and detoxification, enabling wild-type cells to tolerate exogenous zinc concentrations as high as 5 mM. The zinc stored in the vacuole can attain millimolar levels, and can be mobilised under zinc-deficient conditions for use by the cell. Vacuolar zinc uptake is mediated by two members of the cation diffusion facility CDF family, Zrcl and Cotl (Fig. 8.16). 

Zn shows a variety of effects within the nervous system, thereby requiring that levels of zinc are regulated to a very precise level. A fine balance between ion sequestration, intracellular buffering, and extrusion exists in order to maintain cellular zinc homeostasis. A family of proteins known as metallothioneins regulates zinc sequestration and buffering, while zinc uptake and extrusion is mediated by membrane-associated zinc transporters. Mitochondria may serve as the pool of histochemically reactive zinc in neurons and glial cells. 

Organophosphoms compounds, primarily phosphonic acids, are used as sequestrants, scale inhibitors, deflocculants, or ion-control agents in oil wells, cooling-tower waters, and boiler-feed waters. Organophosphates are also used as plasticizers and flame retardants in plastics and elastomers, which accounted for 22% of PCl consumed. Phosphites, in conjunction with Hquid mixed metals, such as calcium—zinc and barium—cadmium heat stabilizers, function as antioxidants and stabilizer adjutants. In 1992, such phosphoms-based chemicals amounted to slightly more than 6% of all such plastic additives and represented 8500 t of phosphoms. Because PVC production is expected to increase, the use of phosphoms additive should increase 3% aimually through 1999. 

Metallothioneins are a group of small proteins (about 6.5 kDa), found in the cytosol of cells, particularly of liver, kidney, and intestine. They have a high content of cysteine and can bind copper, zinc, cadmium, and mercury. The SH groups of cysteine are involved in binding the metals. Acute intake (eg, by injection) of copper and of certain other metals increases the amount (induction) of these proteins in tissues, as does administration of certain hormones or cytokines. These proteins may function to store the above metals in a nontoxic form and are involved in their overall metaboHsm in the body. Sequestration of copper also diminishes the amount of this metal available to generate free radicals. 

Metallothionein was first discovered in 1957 as a cadmium-binding cysteine-rich protein (481). Since then the metallothionein proteins (MTs) have become a superfamily characterized as low molecular weight (6-7 kDa) and cysteine rich (20 residues) polypeptides. Mammalian MTs can be divided into three subgroups, MT-I, MT-II, and MT-III (482, 483, 491). The biological functions of MTs include the sequestration and dispersal of metal ions, primarily in zinc and copper homeostasis, and regulation of the biosynthesis and activity of zinc metalloproteins. 

Stabilizers to either inhibit or control the specific deposition of sulfates, phosphates, phosphonates, silicates, zinc, and other difficult salts in the cooling water. In reality, these are forms of deposit control agents (DCAs) and tend to act as sequestrants, or as dispersants and defloccu-lators for precipitated salts. 

Fig. 1. Schematic overview of copper trafficking and homeostasis inside the yeast cell. The actions of Mad and Ace 1, copper-dependent metalloregulatory transcription factors, control the production of copper import [copper transporter (Ctr) and reductase (Fre)] and detoxification/sequestration [metallothionein (MT)] machineries, respectively. Three chaperone-mediated delivery pathways are shown. Atxl shuttles Cu(I) to the secretory pathway P-type ATPase Ccc2 (right). CCS delivers Cu(I) to the cytoplasmic enzyme copper-zinc superoxide dismutase (SOD) (left). Coxl7 shuttles Cu(I) to cytochrome c oxidase (CCO) in the mitochondria (bottom). Mitochondrial proteins Scol and Sco2 may also play a role in copper delivery to the CuA and CuB sites of CCO. Copper metabolism and iron metabolism are linked through the actions of Fet3, a copper-containing ferroxidase required to bring iron into the cell (lower right) (see text).

Zinc and Zinc Transport and Sequestration Proteins in the Brain in the Progression of Alzheimer s Disease... 

In general, Zn homeostasis is maintained by three families of proteins (a) met-allothioneins (MT) that quickly bind, sequester, and hold Zn after influx into the cytoplasm, (b) Zrt-Irt-like (ZIP) proteins that likely mediate Zn influx into the cell, and (c) zinc transporter (ZnT) proteins that mediate efflux of cytoplasmic Zn to the extracellular space or sequestration in intracellular organelles. 

Palmiter RD, Cole TB, Findley SD (1996) ZnT-2, a mammalian protein that confers resistance to zinc by facilitating vesicular sequestration. EMBO J 15 1784-1791 Peila R, Rodriguez BE, Launer LJ (2002) Type 2 diabetes, APOE gene, and the risk for dementia and related pathologies The Honolulu-Asia Aging Study. Diabetes 51 ... 

Sequestration of zinc ions. Spirocyclopentane (3) was discovered by G. Gustavson (1896) as a product of the action of zinc dust on pentaerythrityl tetrabromide (1) in aqueous ethanol. Later workers, chiefly N. D. Zelinsky (1912) and 1. N. Shokhor (1954) investigated the reaction extensively without finding a way to inhibit extensive p CHzBr... 

Russian workers (1953) had attempted to synthesize spirocyclohexane (9) by reaction of (8) with zinc dust but had isolated only the product of rearrangement, (10). McGreer applied Applequist s sequestration procedure and obtained the... 

There was a moderate adsorption of Al to Fe plaque, and this resulted in reduced Al uptake in plant tissue of Phragmites (Batty et al., 2002). Copper is concentrated in Fe plaque but will preferentially adsorb to Mn if Mn is present in the plaque (St-Cyr and Crowder, 1990 Ye et al., 2001). The sequestration of Cu in the root plaque appears to reduce uptake of Cu by the plant. However, as Cu concentrations build up on the Fe plaque, the amount of Cu transported into the plant tissue can increase (Ye et al., 2001). Zinc can also be concentrated in Fe plaque. For Typha, this effect is more pronounced in the field than in artificial laboratory microcosms (Ye et al., 1998). Several reports have shown... 

Nickel and zinc in soil ferromanganese nodules. One of the most efficient and durable process responsible for trace metal sequestration in soils is the formation of ferromanganese micronodules, which often have been compared to the well-known oceanic Mn nodules (Glasby et al. 1979 White and Dixon 1996 Han et al. 2001) (Fig. 30a). Although soil micronodules are the premier reservoir for many trace elements in soils, the crystal chemistry of the sequestered elements remains unknown. Chemical analyses of individual nodules from Sicilia and New Zealand showed that some elements, such as Co, Ce, Ba, Pb, Ni, are several times to more than one order of magnitude enriched in the concretions relative to the soil matrix, whereas others are less (e g., Zn) or even depleted (Childs 1975 Palumbo et al. 2001) (Fig. 30b). Since nodules are formed in situ within the soil matrix by local enrichment of Fe and Mn oxides, the observed difference of metal enrichment in the concretions relative to the soil matrix likely results from a difference of metal affinity for soil minerals. The micronodule analyzed here by... 

Uses Sequestrant, dispersant for cooling water treatment, industrial cleaners, alkaline cleaners, scale control, and lubricant removal from zinc... 

In this scenario, as a consequence of the maternal acute phase response, there is a marked increase in the synthetic rates of several proteins including MT in maternal liver. The increase in the concentration of MT results in a sequestration of zinc in maternal liver, a drop in plasma zinc, and reduced zinc transfer to the embryo. If the decreased zinc transfer to the embryo occius ditring critical periods of organogenesis, zinc-dependent processes can be disrupted in the growing embryo leading to developmental defects and malformatiorts. ... 

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