Mercury binding region

Hg2 + selectively binds the AT region, apparently due to its great affinity for thymine. Thus, Hg2+ interacts with DNA at nitrogen atoms, replacing hydrogen between the thymine and adenine bases [114]. This interaction results in increased helix stability and an increased diameter of the double helix, approximating the difference between the atomic radius of hydrogen and mercury [116]. 

The enzyme contains six Zn2+ per molecule, two per R subunit. The zinc is not required for catalytic activity, but is essential for the maintenance of the quaternary structure. The structure has been determined to a resolution of 2.8 A in the presence and absence of CTP.528 The zinc-binding site is located in the C-terminal region of the R chains, and involves four cysteinyl residues, with tetrahedral geometry. The zinc domain represents the major site of interaction between the R and C chains, explaining the importance of zinc for the association of the subunits and the dissociative effect of mercurial reagents. When E. coli is grown in a zinc-deficient medium, some 70% of the enzyme is found to be dissociated into subunits.529... 

The dissociation energies of alkali-metal clusters show variations due to even-odd effects and shell closures. This is not the case for mercury. The dissociation energies and the mass spectra show no trace of similar rapid variations. The dot-dashed line is from the tight-binding calculation of Pastor et a/. - for neutral Hg clusters. It deviates from the experimental result already for n = 3 and shows a much smoother transition. The experiment points to a more abrupt transition between the different regions of binding. 

The nephrotoxic potential of mercury is related to its accumulation in the proximal tubule region and the intracellular binding to several functional groups, especially thiols, which results in inactivation of different enzymes and inhibition of protein synthesis... 

Skyllberg, U. L., Bloom, P. R., Nater, E. A., Xia, K., and Bleam, W. F. (1997). Binding of mercury(II) by reduced sulfur in soil organic matter. In Extended Abstracts, 4th International Conference on the Biogeochemistry of Trace Elements, June 23—26 1997, Berkeley, CA, U.S. Army Cold Regions Research and Engineering Laboratory, Hanover, NH, 285-286. 

Mercury (Hg) Contaminated fish (especially from the Great Lakes region of the United States) Binds to sulfur-containing molecules in organelles can cause neurological damage, death Toxic... 

Many bacteria are resistant to inorganic and organic mercury compounds. Mercuric reductase (MerA) is a key enzyme in the mercury detoxification pathway. MerA catalyzes the NADPH-dependent reduction of Hg to its volatile, uncharged, elemental state (Hg ). MerA is a cytosolic protein that is homologous to GR, but also has a short C-terminal extension and a long N-terminal extension not found in GR. MerA contains three pairs of cysteines one in the C-terminal extension, one in the N-terminal extension, and one in the GR-like region of the protein. The N-terminal domain binds one molecule of mercury and delivers it to the catalytic core of the protein, made up of the GR-like portion and the C-terminal extension, where it is reduced. The disulfide from... 

An additional feature in Fig. 2 worth noting is the amino-terminal 160 amino acids of mercuric reductase that lacked a fixed position in the crystal and therefore were not part of the solved structure. These contain the sequence that is homologous to MerP and postulated to be a mercurybinding domain. This region is drawn in Fig. 2 as an extension from the protein perhaps it functions like a baseball mitt that catches Hg from the membrane transport proteins and delivers Hg " to the carboxyl-terminal catalytic binding site, so that, as in the bucket brigade model above, Hg " is never found free within the cell. Mutant strains with the transport system but lacking the MerA detoxification enzyme are hypersensitive to mercury salts, as they accumulate Hg " but cannot get rid of it. After reduction by NADH (via FAD and the active site cysteine pair), metallic Hg is released... 

G—C rich regions of DNA, in contrast to mercury, and separation founded on this basis can also be achieved [103]. Again a crystal structure of l-(methylcytosine)silver(I) nitrate may serve as model for the DNA interaction [104]. This complex is also of interest because of its dimeric nature. The proposed inhibition of bacterial DNA synthesis by the Ag" ion (Chapter 9) is relevant here, although no attempts appear to have been made to correlate cytotoxicity with modes of binding. 

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