Detoxification cadmium

Aiking, H., Stijnman, A., van Garderen, C., van Heerikhuizen, H. van t Riet, J. (1984). Inorganic phosphate accumulation and cadmium detoxification in Klebsiella aerogenes NCTC 418 growing in continuous culture. Applied and Environmental Microbiology, 47, 374-7. 

Given the state of the ion, one would expect the coordination chemistry of this metal ion to be dominated by examples of coordination to four two-electron donors. In this sense, the ligands containing thiolate or carboxylate groups are interesting to mimic zinc-thiolate or zinc-carboxylate active sites, which play a relevant role in bioinorganic chemistry and in the field of cadmium detoxification by chelation. 

Metallothioneins (MTs) are a superfamily of low-molecular-weight (<7000-dalton) intracellular metal-binding proteins, which, in many species, play a critical role in (a) the detoxification of nonessential metals such as Cd2+ and Hg2+ and (b) the regulation of intracellular concentrations of essential metals such as Zn2+ and Cu+. In 1957, Kagi and Vallee first purified and characterized MT as a cadmium-binding protein in equine kidney. 

In plants, two kinds of metal-binding peptides or proteins are synthesized. Plant metallothioneins are inducible cysteine-rich entities very like those found in animals. Differential expression (induction) of metallothionein genes can be due to both variation of external heavy metal concentrations and the influence of various environmental factors. The principle role of plant metallothioneins seems to be in homeostasis rather than in metal detoxification. Plants are also known to have so-called phytochelatins, which are non-protein thiols specifically induced upon exposure to heavy metals. A close positive relationship between the concentrations of cadmium and phytochelatins in the plant shoot material has been observed and linked to the degree of growth inhibition (Keltjens and Van Beu-sichem, 1998). These observations make the use of phytochelatins promising for the assessment of heavy metal effect on plants. 

Elarry A., Elarrie G. and Jan van t R. (1985) Detoxification of mercury, cadmium and lead in Klebsielle aerogenes NCTC 418 growing in continuous culture. Appl Environ Microbiol 50 1262-1267. 

Mercury showed the highest toxicity of all metals examined (Nies 1999). The Hg(II) cation diffuses into the cells as a hydroxo-complex and adheres to thiols. For efficient detoxification, Hg(II) is actively imported into bacterial cells and reduced to the metallic form, which then diffuses out of the cell and its environment. Due to their toxicity, mercury is not a trace element, and cadmium is only one under rare conditions (Brown et al. 2002a). 

A number of zinc proteins have been described, the functions of which have not yet been fully identified. Of particular interest are the metallothioneins these are sulfur-rich proteins of low molecular weight and are rich in cadmium, zinc, and possibly other bivalent metals. It is suggested that the metallothioneins play a role in metal metabolism and detoxification (Kagi and Nordberg 1979, Foulker 1982, Hamer 1986). 

Almar MA, Diaz-Mayans J, Romero FJ (1987) Glutathione content and GSH S-transferase activity in midgut gland of Procambrus clarkii. Sex differences, the effect of fasting, and their implications in cadmium toxicity. Comp Biochem Physiol 87C 433-435 Al-Sabti K, Kurelec B (1985) Induction of chromosomal aberrations in the mussel Mytilus gallo-provincialis watch. Bull Environ Contam Toxicol 35 660-665 Allsop TF (1985) Comparative detoxification of phenols by some marine invertebrates. Masters thesis, Victoria Univ Wellington... 

There are two isomers of metallothionein in mammalian cells MT-1 and MT-2. There are several metallothionein genes. The transcription of each is controlled by several heavy-metal response elements or by hormone response elements [14,15]. The mechanism of control of the metallothionein genes by its promoters is a subject of intense investigation. Despite all the knowledge gained so far, the function of the metallothionein is still uncertain. However, it appears that the metallothionein may play key roles in the homeostasis of zinc within cells and in the detoxification of excess copper or toxic nonessential metals like cadmium and mercury. 

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