EXAFS studies of metallothionein

Charnock, John; Garner, C. David; Abrahams, I.; Arber, Judith M.; Hasnain, S.S.; Henehan, Colin J.; Vašák, Milan

doi:10.1016/0921-4526(89)90210-x

Cited by 4 publications

(3 citation statements)

References 8 publications

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“…On the contrary, EXAFS studies have failed to give consistent results for second shell scattering. For example, EXAFS studies on Zn7MT (MT complexed with 7 Zn atoms) extracted from rabbit liver supported the NMR results and showed two higher Zn-Zn shells at 5.0 and 5.2 Å, with a coordination number of 1 for both shells (48,32). Data from Stephan and Hitchcock (53) on model compounds for MT [Zn4(SC6H5)10 2-] also indicated the presence of a Zn-Zn second-shell peak at R ) 4.03 Å and CN ) 3.6.…”

Section: Table 2 Zn K-edge Energies Determined From Xanes For Fish Li...mentioning

confidence: 74%

“…113 Cd NMR studies on MTs extracted from rat or blue crab suggested that each metal ion was complexed with four thiolate ligands (26,28,29). Supporting results from EXAFS studies of Zn in different Zn-induced MTs extracted from sheep, pig, or rabbit livers also indicated that the metal atoms were exclusively bonded to four S atoms from the cysteinyl group in the protein (30)(31)(32). However, specific intracellular interactions of metal with MTs or other ligands in fish still need to be clarified (33), and more direct, spectroscopic evidences of metal speciation in fish tissue are required.…”

Section: Introductionmentioning

confidence: 98%

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Speciation of Hepatic Zn in Trout Exposed to Elevated Waterborne Zn Using X-ray Absorption Spectroscopy

Beauchemin

Hesterberg

Nadeau

et al. 2004

Environ. Sci. Technol.

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The long-term impacts of chronic metal exposure for aquatic biota are not well understood, partly due to a lack of understanding of metal speciation within tissues. The objective of this study was to determine hepatic Zn speciation of rainbow trout (Oncorhnychus mykiss) exposed to Zn-enriched water in relation to unexposed (control) fish,through direct analysis of freeze-dried liver samples using synchrotron X-ray absorption spectroscopy (XAS). Juvenile rainbow trout (n=30) were exposed to Zn in a two-step process, 200 microg L(-1) for 14 days, followed by 370 microg L(-1) for 23 days. Thirty other trout were grown in a control treatment (10 microg Zn L(-1)). At the end of the experiment, three liver samples per treatment were collected, freeze-dried, ground, and mixed homogeneously. Although Zn concentration was higher in the Zn-exposed livers than in the control livers (22.32 vs 13.73 mg kg(-1), respectively; p < 0.05), Zn speciation was similar for both groups. Extended X-ray absorption fine structure (EXAFS) spectroscopy indicated that Zn was coordinated to 4 sulfur atoms with an average Zn-S bond distance of 2.31 +/- 0.02 A. Sulfur K-XANES analysis confirmed that S was predominantly in reduced organic form analogous to cysteine. Our results are consistent with previous evidence for Zn(II) bonding to S in metallothionein proteins. These results suggest that the mechanisms for dealing with the extra load of bioaccumulated Zn in high exposure conditions were the same as in the control group.

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Section: Table 2 Zn K-edge Energies Determined From Xanes For Fish Li...mentioning

confidence: 74%

Section: Introductionmentioning

confidence: 98%

Speciation of Hepatic Zn in Trout Exposed to Elevated Waterborne Zn Using X-ray Absorption Spectroscopy

Beauchemin

Hesterberg

Nadeau

et al. 2004

Environ. Sci. Technol.

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“…However, on the basis of X‐ray absorption studies conducted on some of the species observed in the titration of either apo‐MT or Zn 7 ‐MT with Hg(II), monitored by optical spectroscopy, Lu & Stillman [17] proposed a distorted tetrahedral co‐ordination for Hg(II) in Hg 7 ‐MT with two short (2.33 Å) and two long (3.4 Å) Hg‐S distances [18]. Previous extended X‐ray absorption fine structure (EXAFS) results for Hg 7 ‐MT were consistent with a Hg‐S bond length of 2.42 Å and suggested that Hg(II) was in a three‐co‐ordinate thiolate environment [19].…”

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confidence: 96%

Mercury(II) binding to metallothioneins

Leiva‐Presa

Capdevila

González-Duarte

2004

European Journal of Biochemistry

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With the aim of extending our knowledge on the reaction pathways of Zn-metallothionein (MT) and apo-MT species in the presence of Hg(II), we monitored the titration of Zn 7 -MT, Zn 4 -aMT and Zn 3 -bMT proteins, at pH 7 and 3, with either HgCl 2 or Hg(ClO 4 ) 2 by CD and UV-vis spectroscopy. Detailed analysis of the optical data revealed that standard variables, such as the pH of the solution, the binding ability of the counter-ion (chloride or perchlorate), and the time elapsed between subsequent additions of Hg(II) to the protein, play a determinant role in the stoichiometry, stereochemistry and degree of folding of the Hg-MT species.Despite the fact that the effect of these variables is unquestionable, it is difficult to generalize. Overall, it can be concluded that the reaction conditions [pH, time elapsed between subsequent additions of Hg(II) to the protein] affect the structural properties more substantially than the stoichiometry of the Hg-MT species, and that the role of the counter-ion becomes particularly apparent on the structure of overloaded Hg-MT.Keywords: mercury(II) binding; mercury-metallothionein; metallothionein; a-metallothionein; b-metallothionein.Mercury thiolates provide representative examples of the structural diversity shown by the extensive family of metal thiolates [1][2][3][4]. The most striking features of mercury thiolates in the solid phase are the different structures obtained when Hg(II) is co-ordinated to very similar thiolate ligands [5,6] and the distinctive behavior of Hg(II) towards a particular thiolate compared with that of Zn (II) or Cd(II) [7], which has been referred to as the zinc family paradox [3]. Moreover, correlations between solid-state and solution complexes cannot be easily established. Overall, the diverse co-ordination preferences of Hg(II) ions (mainly tetrahedral, trigonal-planar and digonal) and their coexistence in polynuclear complex species, the various ligation modes of the thiolate ligands (i.e. terminal, l 2 -bridging or l 3 -bridging) and the possibility of secondary Hg(II)-sulfur interactions [8] make it difficult to anticipate the structure of a particular mercury thiolate complex [1,3,9]. This results from the interplay of not only the above factors, but also the reaction conditions. Of these, the presence of additional coordinating species, such as halide ions, make the bonding situation for mercury even less straightforward than in the case of homoleptic mercury thiolates [10,11].The biological chemistry of mercury is dominated by co-ordination to cysteine thiolate groups in agreement with the preference of this metal ion for the soft sulfur ligands. The high binding constants for binding of Hg(II) to cysteine residues account for the irreversible replacement of essential metals (Zn, Cu) in cysteine-containing metalloproteins and thus for the high toxicity of mercury to living systems. Within the same context of the highly favored thermodynamically Hg-S bond, resistance to Hg(II) toxicity in several bacteria is based on an ensemble of prote...

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X-ray absorption spectroscopy of biological molecules

Garner¹

1990

Applications of Synchrotron Radiation

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EXAFS studies of metallothionein

Cited by 4 publications

References 8 publications

Speciation of Hepatic Zn in Trout Exposed to Elevated Waterborne Zn Using X-ray Absorption Spectroscopy

Speciation of Hepatic Zn in Trout Exposed to Elevated Waterborne Zn Using X-ray Absorption Spectroscopy

Mercury(II) binding to metallothioneins

X-ray absorption spectroscopy of biological molecules

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