Zinc detoxification

Zinc is also toxic (Nies 1999). The high bioavailability of zinc makes it very probable for microbes to encounter toxic zinc concentration (Nies 2000). Therefore, zinc-detoxification systems which rely on efflux (P-,... 

Pamukcu S, Khan LI, Fang H-Y. (1990). Zinc detoxification of soils by electro-osmosis. Transportation Research Record 1288 41 6. 

FSM Sosnowiec manufactures automobile lamps, door locks, and window winders for the Polish-manufactured Fiat cars. The lamp bodies are made of zinc-aluminum alloy and then copper-nickel-chromium plated. The door locks and window winders are made of steel and then zinc plated. The wastestreams contain cyanide and the heavy metals chromium (VI), copper, zinc, and nickel. The company carries out the traditional treatments of detoxification, neutralization, and dewatering.29... 

Copper is part of several essential enzymes including tyrosinase (melanin production), dopamine beta-hydroxylase (catecholamine production), copper-zinc superoxide dismutase (free radical detoxification), and cytochrome oxidase and ceruloplasmin (iron conversion) (Aaseth and Norseth 1986). All terrestrial animals contain copper as a constituent of cytochrome c oxidase, monophenol oxidase, plasma monoamine oxidase, and copper protein complexes (Schroeder et al. 1966). Excess copper causes a variety of toxic effects, including altered permeability of cellular membranes. The primary target for free cupric ions in the cellular membranes are thiol groups that reduce cupric (Cu+2) to cuprous (Cu+1) upon simultaneous oxidation to disulfides in the membrane. Cuprous ions are reoxidized to Cu+2 in the presence of molecular oxygen molecular oxygen is thereby converted to the toxic superoxide radical O2, which induces lipoperoxidation (Aaseth and Norseth 1986). 

When animals are fed experimental diets lacking copper or zinc, their copper or zinc status rapidly declines, suggesting that there is not a storage pool of these metals. Thus, while the small, cysteine-rich protein metallothionein (see below) can avidly bind zinc and copper, this may reflect its role in detoxification rather than as a specific storage form. This is reflected by the fact that metallothionein genes are typically expressed at a basal level, but their transcription is strongly induced by heavy metal load. 

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).

Another common biomarker for trace metal exposure is the metal-binding protein metallothionein, which regulates normal zinc and copper metabolism and provides a mechanism for metal detoxification. Changes in metallothionein activity provide a sensitive marker of trace metal exposure. 

Prasad, G.K., Mahato, T.H., Singh, B., Ganesan, K., Pandey, P., Sekhar, K. (2007a). Detoxification reactions of sulphur mustard on the surface of zinc oxide nanosized rods. J. Hazard. Mater. 149 460. ... 

Zinc assumes a special role in the intrahepatic formation of retinol-binding protein, which is essential for the release of vitamin A into the blood. Zinc deficiency results in a decrease in RBR Furthermore, as a part of ADH, zinc is crucial for alcohol degradation in the hepatocytes and for enzyme activation in the detoxification of ammonia in the urea cycle, (s. fig. 3.12 )... 

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). 

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