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Formation of Mercury(II)-Glutathione Conjugates Examined Using High Mass Accuracy Mass Spectrometry.

Fine Z, Wood TD - Int J Anal Mass Spectrom Cromatogr (2013)

Bottom Line: While the 1:1 Hg(II):GSH conjugate is not formed immediately upon mixing aqueous solutions of Hg(II) and GSH, two species containing Hg(II) are observed: the 1:2 Hg(II):GSH conjugate, [(GS)2Hg + H(+)], and a second Hg(II)-containing species around m/z 544.Interestingly, this species at m/z 544 decreases in time while the presence of the 1:1 Hg(II):GSH conjugate increases, suggesting that m/z 544 is an intermediate in the formation of the 1:1 conjugate.Further confirmation of [GSH + HgCl](+) is supported by collision of induced dissociation experiments, which show neutral loss of HCl from the intermediate and loss of the N- and C-terminal amino acids, indicating binding of Hg(II) at the Cys residue.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Chemical and Biological Engineering, University at Buffalo, State University of New York, Buffalo, USA.

ABSTRACT

Maternal exposure to Hg(II) during pregnancy has been identified as a potential causal factor in the development of severe neurobehavioral disorders. Children with autism have been identified with lower reduced glutathione (GSH)/oxidized glutathione (GSSG) ratios, and GSH is known to strongly bind Hg(II). In order to gain insight into the mechanism by which GSH binds Hg(II), high resolution mass spectrometry coupled with tandem mass spectrometry was utilized to examine the conjugation process. While the 1:1 Hg(II):GSH conjugate is not formed immediately upon mixing aqueous solutions of Hg(II) and GSH, two species containing Hg(II) are observed: the 1:2 Hg(II):GSH conjugate, [(GS)2Hg + H(+)], and a second Hg(II)-containing species around m/z 544. Interestingly, this species at m/z 544 decreases in time while the presence of the 1:1 Hg(II):GSH conjugate increases, suggesting that m/z 544 is an intermediate in the formation of the 1:1 conjugate. Experiments using the high mass accuracy capability of Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry coupled to an electrospray ionization source indicate that the intermediate species is [GSH + HgCl](+), and not the 1:1 conjugate [Hg(GSH) - H + 2H2O](+) postulated in previous literature. Further confirmation of [GSH + HgCl](+) is supported by collision of induced dissociation experiments, which show neutral loss of HCl from the intermediate and loss of the N- and C-terminal amino acids, indicating binding of Hg(II) at the Cys residue.

No MeSH data available.


Related in: MedlinePlus

CID(12V) of the m/z 544 cluster generated by ESI-FTICR.
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Figure 3: CID(12V) of the m/z 544 cluster generated by ESI-FTICR.

Mentions: To validate that chlorine was indeed present in this species, we conducted MS/MS using CID. The entire isotopic cluster centered about m/z 544 was mass-selected in the source quadrupole of the SolariX FT-ICR and dissociated with argon gas in the collision cell before transport to the FT-ICR ion trap. CID experiments were conducted over the range 8 – 16 V, but the product ions generated only showed small differences in relative abundance and not in the actual product ions produced, so only the 12 V CID result is shown in Figure 3. CID confirms that chlorine is present in the formula for m/z 544; neutral loss of 35.9764 Da is observed, corresponding to loss of HCl. The neutral loss of 111.0079 Da is due to the loss of glycine hydrochloride from the C-terminus of GSH, which is followed by subsequent neutral losses of H2O and NH3, respectively. The peak at m/z 379.0032 Da is consistent with the loss of the N-terminal μ-glutamic acid residue [17,18] from the m/z 508 product ion, while m/z 306.0756 corresponds to GS+; these results completely support a previously reported dissociation mechanism of the 1:1 Hg(II):GSH conjugate [9].


Formation of Mercury(II)-Glutathione Conjugates Examined Using High Mass Accuracy Mass Spectrometry.

Fine Z, Wood TD - Int J Anal Mass Spectrom Cromatogr (2013)

CID(12V) of the m/z 544 cluster generated by ESI-FTICR.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4442495&req=5

Figure 3: CID(12V) of the m/z 544 cluster generated by ESI-FTICR.
Mentions: To validate that chlorine was indeed present in this species, we conducted MS/MS using CID. The entire isotopic cluster centered about m/z 544 was mass-selected in the source quadrupole of the SolariX FT-ICR and dissociated with argon gas in the collision cell before transport to the FT-ICR ion trap. CID experiments were conducted over the range 8 – 16 V, but the product ions generated only showed small differences in relative abundance and not in the actual product ions produced, so only the 12 V CID result is shown in Figure 3. CID confirms that chlorine is present in the formula for m/z 544; neutral loss of 35.9764 Da is observed, corresponding to loss of HCl. The neutral loss of 111.0079 Da is due to the loss of glycine hydrochloride from the C-terminus of GSH, which is followed by subsequent neutral losses of H2O and NH3, respectively. The peak at m/z 379.0032 Da is consistent with the loss of the N-terminal μ-glutamic acid residue [17,18] from the m/z 508 product ion, while m/z 306.0756 corresponds to GS+; these results completely support a previously reported dissociation mechanism of the 1:1 Hg(II):GSH conjugate [9].

Bottom Line: While the 1:1 Hg(II):GSH conjugate is not formed immediately upon mixing aqueous solutions of Hg(II) and GSH, two species containing Hg(II) are observed: the 1:2 Hg(II):GSH conjugate, [(GS)2Hg + H(+)], and a second Hg(II)-containing species around m/z 544.Interestingly, this species at m/z 544 decreases in time while the presence of the 1:1 Hg(II):GSH conjugate increases, suggesting that m/z 544 is an intermediate in the formation of the 1:1 conjugate.Further confirmation of [GSH + HgCl](+) is supported by collision of induced dissociation experiments, which show neutral loss of HCl from the intermediate and loss of the N- and C-terminal amino acids, indicating binding of Hg(II) at the Cys residue.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Chemical and Biological Engineering, University at Buffalo, State University of New York, Buffalo, USA.

ABSTRACT

Maternal exposure to Hg(II) during pregnancy has been identified as a potential causal factor in the development of severe neurobehavioral disorders. Children with autism have been identified with lower reduced glutathione (GSH)/oxidized glutathione (GSSG) ratios, and GSH is known to strongly bind Hg(II). In order to gain insight into the mechanism by which GSH binds Hg(II), high resolution mass spectrometry coupled with tandem mass spectrometry was utilized to examine the conjugation process. While the 1:1 Hg(II):GSH conjugate is not formed immediately upon mixing aqueous solutions of Hg(II) and GSH, two species containing Hg(II) are observed: the 1:2 Hg(II):GSH conjugate, [(GS)2Hg + H(+)], and a second Hg(II)-containing species around m/z 544. Interestingly, this species at m/z 544 decreases in time while the presence of the 1:1 Hg(II):GSH conjugate increases, suggesting that m/z 544 is an intermediate in the formation of the 1:1 conjugate. Experiments using the high mass accuracy capability of Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry coupled to an electrospray ionization source indicate that the intermediate species is [GSH + HgCl](+), and not the 1:1 conjugate [Hg(GSH) - H + 2H2O](+) postulated in previous literature. Further confirmation of [GSH + HgCl](+) is supported by collision of induced dissociation experiments, which show neutral loss of HCl from the intermediate and loss of the N- and C-terminal amino acids, indicating binding of Hg(II) at the Cys residue.

No MeSH data available.


Related in: MedlinePlus