Metallothioneins cobalt

The protein metallothionein (MT) has a MW of 6000 and is rich in thiolate groups. It binds up to seven zinc(II), cadmium(II) and cobalt(II) ions. The seven ions are organized in two clusters. The so-called M4S11 cluster is shown in... 

The metabolism of zinc is influenced by hormones, stress situations, lipopolysaccharides, toxins, oxygen radicals, lipid peroxidations, etc. This may lead to fluctuations in the zinc concentration, mainly due to the induction of metallothioneine (MT), which is a transport and intracellular depot protein. One third of this protein consists of cysteine, which binds zinc, copper, cadmium, cobalt and mercury. This protects the body from toxic heavy metal... 

Metallothioneins are a unique and widely distributed group of proteins. They are characterized by their low molecular weight (—6000), high cysteinyl content, and the ability to bind substantial numbers of metal ions (43). The proteins bind copper and zinc, thereby providing a mobile pool as part of the normal metabolism of these elements, and offer protection from the invasion of inorganic forms of the toxic elements cadmium, lead, and mercury. In addition, other metals, such as iron and cobalt, can be induced to bind. XAS is ideally suited to probe the environment of these different metal atoms (see Fig. 1), and the structural interpretations obtained from an analysis of the EXAFS data obtained in several such studies are summarized in Table 1(44). Thus, in each case, the data are consistent with the primary coordination of the metal deriving from the cysteinyl residues. 

See also Aluminum Antimony Arsenic Barium Beryllium Bismuth Boron Cadmium Cesium Chromium Cobalt Copper Gallium Iron Lead Lithium Manganese Mercury Metallothionein Molybdenum Nickel and Nickel Compounds Platinum Potassium Selenium Silver Sodium Tellurium Thallium Tin Titanium Tungsten Uranium Vanadium Zinc. 

Metallothioneins, especially in higher animals, are small proteinsrich in cysteine (20 per molecule) and devoid of the aromatic amino acids phenylalanine and tyrosine. The cysteine residues are distributed throughout the peptide chain. However, in the native form of the protein (Figure 1.10), the peptide chains fold to produce two clusters of —SH, which bind either three or four atoms of zinc, cadmium, cobalt, mercury, lead, or nickel. Copper binding is distinct from zinc, with 12 sites per molecule. 

The absorption spectrum of cadmium LADH differs markedly from that of the zinc or cobalt enzyme and perhaps bears upon the nature of the metal-binding ligands (Figure 19). An intense band centered at 245 m/i with a molar absorptivity per cadmium atom of 10,200 is shown by the difference spectrum at the bottom of the figure zinc LADH is employed as the reference. Notably, the molar absorptivity of this band is nearly 14,000, close to that reported for the cadmium mercaptide chromophores of metallothionein (23). This is consistent with the hypothesis that sulfhydryl groups may serve as metal ligands in LADH. 

Transport of nidcel, manganese, cobalt and vanadium. 2.4 Storage of transition metals and zinc. Metallothionein Transport of Iron in Microorganisms. 3.1 Multiple pathways for iron transport The catecholaie siderophores The hydroxamate siderophores Pseudobactin... 

Physiologically important metal ions include iron, copper, cobalt and nickel. Normally, metal ions are not present in free solution to any significant extent, but are bound to transport proteins (in plasma) or storage proteins and enzymes (in cells). Thus, iron is bound to transferrin (in plasma) and haemosiderin and ferritin in tissues, copper is bound to caeruloplasmin in plasma, and metallothionein in plasma binds a wide variety of metal ions. The adverse effects of iron overload (section 4.5.1) are the result of free iron, not bound to storage proteins, acting as a source of oxygen radicals. 

Cadmium is a toxic element (see Chapters 1,14,15) that accumulates especially in kidney and liver [4] being bound preferably to metallothionein (Chapters 6,11). On the other hand, the chemical similarity of Cd " " to Zn " is confirmed by the fact that carbonic anhydrase of marine phytoplankton contains Cd (Chapter 16), whereas the corresponding zinc enzymes are found in organisms from aU kingdoms [5] catalyzing the reversible hydration of carbon dioxide. In marine diatoms cadmium, cobalt, and zinc can functionally substitute for one another to maintain optimal growth [6]. Cadmium-carbonic anhydrase is involved in the acquisition of inorganic carbon for photosynthesis [6]. 

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