Zinc uptake

It has been demonstrated that extremely tight control is exhibited over the intracellular zinc concentrations by the metalloregulatory proteins controlling zinc homeostasis. It had previously been thought that intracellular zinc was available in a pool of free zinc ions in the micro- to pico-molar concentration. An important study shows that these concentrations of free zinc are inconsistent with the concentrations required to trigger zinc uptake.974... 

LeClaire, J.P., Change A.C., Levesque C.S, Sposito G. Trace metal chemistry in arid-zone field soils amended with sewage sludge. IV Correlations between zinc uptake and extracted soil zinc fractions. Soil Sci Soc Am J 1984 48 509-513. 

Saccharomyces cerevisiae 85 copper uptake 290 iron storage 100 zinc uptake 295 scandium 108 selenium xvii... 

In the Gram-positive bacterium Bacillus subtilis (DNA with low G + C content), three Fur-like proteins have been characterized (Bsat et al., 1998). One, called Fur, regulates mainly iron uptake and siderophore biosynthesis. A second one, called PerR, regulates peroxide stress response genes and acts with manganese as corepressor. A third one, Zur, regulates genes for zinc uptake. The Zur protein found in E. coli shows only 25 % identity to the B. subtilis Zur, while the two Fur proteins have 32 % identical amino acids. 

Transport proteins (channels) for chloride and zinc Vacuolar proton pump Components of synaptic vesicles to mediate the chloride flux for glutamate uptake and zinc uptake in most synaptic vesicles. Zinc transporter is homologous to endosomal and plasma membrane zinc transporters chloride transporters remain to be identified. Protein complex of more than 12 subunits. Constitutes the largest component of synaptic vesicles and establishes... 

Bervoets, L., R. Blust, and R. Verheyen. 1996. Effect of temperature on cadmium and zinc uptake by the midge larvae Chironomus riparius. Arch. Environ. Contam. Toxicol. 31 502-511. 

Extractable concentrations of sediment-bound zinc were positively correlated with zinc concentrations in deposit feeding clams (Luoma and Bryan 1979). Availability of sediment zinc to bivalve molluscs was higher at increased sediment concentrations of amorphous inorganic oxides or humic substances, and lower at increased concentrations of organic carbon and ammonium acetate-soluble manganese. Zinc uptake by euryhaline organisms was enhanced at low water salinity (Luoma and Bryan 1979). 

Zinc added to the ambient water depressed copper accumulations in tissues of juvenile catfish (Clarias lazera), but copper added to the medium depressed zinc uptake (Hilmy et al. 1987b). A similar situation was reported in barnacles (Elminus modestas) however, simultaneous exposure to copper and zinc resulted in enhanced uptake of both metals (Elliott et al. 1985). 

Sensitive terrestrial plants die when soil zinc levels exceed 100 mg/kg or when plant zinc content exceeds 178 mg/kg DW (Table 9.5). The phytotoxic zinc level for barley (Hordeum vulgare) is not known, but zinc content of barley leaf rarely exceeds 100 mg/kg DW (Chang et al. 1983). Uptake of zinc from soils by plants depends on soil type for example, uptake is lower in coarse loamy soils than in fine loamy soils (Chang et al. 1983). Zinc uptake by barley leaf is greater with increasing rate of sludge application, but the relation is not proportional (Table 9.5). 

Nugegoda, D. and P.S. Rainbow. 1988a. Effect of a chelating agent (EDTA) on zinc uptake and regulation by Palaemon elegans (crustacea decapoda). Jour. Mar. Biol. Assoc. U.K. 68 25-40. 

Nugegoda, D. and P.S. Rainbow. 1989c. Zinc uptake and regulation breakdown in the decapod crustacean... 

Likewise, for zinc, bacteria have developed active uptake systems (Hantke, 2001). In many bacteria the high-affinity Zn2+ uptake system uses an ABC transporter of the cluster 9 family, which mostly transports zinc and manganese and is found in nearly all bacterial species. First identified in cyanobacteria and pathogenic streptococci, but also found in E. coli, the system is encoded by three genes ZnuABC and consists of an outer membrane permease ZnuB, a periplasmic-binding protein ZnuA and a cytoplasmic ATPase ZnuC. Low-affinity transporters of the ZIP family, described later in this chapter, such as ZupT, have also been shown to be involved in bacterial zinc uptake. 

In plants zinc uptake involves members of the ZIP family, some of which are root specific, while others are found in both roots and shoots. 

Fur is itself part of the family of gene regulatory proteins throughout many bacterial species. The major subclass is mainly involved, like Fur in E. coli, in the control of iron homeostasis, but it can also function in acid tolerance and protection against oxidative stress. Fur also controls the iron-regulated expression of bacterial virulence determinants. One class of the Fur family, Zur, is involved in the regulation of zinc uptake (see below). 

As we saw in Chapter 7, zinc uptake in plants involves proteins of the ZIP family, some of which are root specific while others are found in both roots and shoots. The transport of zinc from the cytosol in many organisms is often associated with members of the cation diffusion facility (CDF) family. Although there are 12 predicted family members in Arabidopsis, only one, MTP1, has been characterized, which seems to function in the transport of Zn into the vacuole. Two members of the heavy metal ATPase (HMA) family, HMA2 and HMA4, have been shown to function in the transport of zinc out of the cells across the plasma membrane. 

Hantke, K. (2005) Bacterial zinc uptake and regulators, Curr. Opin. Microbiol., 8, 196-202. 

Otte ML, Rozema 1, Koster L, Haarsma MS, Broekman RA. 1989. Iron plaque in roots of Aster tripolium L. interaction with zinc uptake. New Phytologist 111 309-317. 

Reid RJ, Brookes JD, Tester MA, Smith FA. 1996. The mechanism of zinc uptake in plants-Characterisation of the low-affinity system. Planta 198 39-45. 

Gunshin, H., Noguchi, T., and Naito, H. (1991). Effect of calcium on the zinc uptake by brush border membrane vesicles isolated from the rat small intestine. Agric. Biol. Client. 55, 2813-2816. 

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