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Ingrid J Pickering

Publications and source records attributed to Ingrid J Pickering.

25 records · Page 2Linked to original sources
PubMed2002

Synthesis, purification, and structural characterization of the dimethyldiselenoarsinate anion.

A novel arsenic-selenium solution species was synthesized by reacting equimolar sodium selenite and sodium dimethylarsinate with 10 mol equiv of glutathione (pH 7.5) in aqueous solution. The solution species showed a single (77)Se NMR resonance at 112.8 ppm. Size-exclusion chromatography (SEC) using an inductively coupled plasma atomic emission spectrometer (ICP-AES) as the simultaneous arsenic-, selenium-, sulfur-, and carbon-specific detector revealed an arsenic-selenium moiety with an As:Se molar ratio of 1:2. Electrospray ionization mass spectrometry (ESI-MS) of the chromatographically purified compound showed a molecular mass peak at m/z 263 in the negative ion mode. Fragmentation of the parent ion (ESI-MS-MS) produced (CH(3))(2)As(-) and Se(2)(-) fragments. Arsenic and selenium extended X-ray absorption fine structure spectroscopy (EXAFS) of the purified species revealed two As-C interactions at 1.943 A and two As-Se interactions at 2.279 A. On the basis of these results this novel solution species is identified as the dimethyldiselenoarsinate anion.

Chromatography, Gel↗
PubMed2002

Pb EXAFS studies on DNA quadruplexes: identification of metal ion binding site.

Nucleic acid quadruplexes are composed of guanine quartets stabilized by specific metal ions. X-ray diffraction can provide high-resolution information on the structure and metal binding properties of quadruplexes, but only if they can be crystallized. NMR can provide detailed information on the solution structure of such quadruplexes but little quantitative data concerning the metal binding site. Here we apply extended X-ray absorption fine structure (EXAFS) measurements to characterize the metal ion binding site, in frozen solution, of the unimolecular quadruplex formed by the thrombin binding aptamer, d(G(2)T(2)G(2)TGTG(2)T(2)G(2)) (TBA), in the presence of Pb(2+) ions. The Pb L(III) -edge X-ray absorption spectrum of this metal-DNA complex is very similar to that we obtain for a Pb(2+)-stabilized quartet system of known structure constructed from a modified guanine nucleoside (G1). The Fourier transforms of the Pb(2+) complexes with both TBA and G1 show a first-shell interaction at about 2.6 A, and a weaker, broader shell at 3.5-4.0 A. Quantitative analysis of the EXAFS data reveals the following: (i) very close agreement between interatomic distances at the metal coordination site for the Pb(2+)-G1 complex determined by EXAFS and by X-ray crystallography; (ii) similarly close agreement between interatomic distances measured by EXAFS for the Pb(2+)-G1 and Pb(2+)-TBA complexes. These results provide strong evidence for binding of the Pb(2+) ion in the region between the two quartets in the Pb(2+)-TBA complex, coordinated to the eight surrounding guanine O6 atoms. The specific binding of Pb(2+) to DNA examined here may be relevant to the genotoxic effects of this environmentally important heavy metal. Furthermore, these results demonstrate the utility of EXAFS as a method for quantitative characterization of specific metal binding sites in nucleic acids in solution.

Binding Sites↗
PubMed2002

The active site of arsenite oxidase from Alcaligenes faecalis.

Arsenite oxidase, a member of the DMSO reductase family of molybdenum enzymes, has two molecules of guanosine dinucleotide molybdenum cofactor coordinating the molybdenum at the active site. X-ray absorption spectroscopy indicates that the Mo-S bonds shorten from 2.47 to 2.37 A upon reduction with the physiological substrate. It also indicates the presence of an oxo ligand at 1.70 A in both oxidized and reduced forms of the enzyme, together with a short, 1.83 A, Mo-O bond in the oxidized form that is lost upon reduction. Resonance Raman spectroscopy indicates that the two pterin dithiolene moieties have different aromaticities, with one, the Q-pterin, having a more discrete dithiolate structure while the other, the P-pterin, has considerable pi-delocalization. Our results indicate that the structure of arsenite oxidase is intermediate between that seen in other molybdenum enzymes, in which one ligand to the metal is provided by the polypeptide (serine, cysteine, or selenocysteine), and tungsten enzymes that lack a peptide ligand.

Alcaligenes↗
PubMed2002

Structures of the cuprous-thiolate clusters of the Mac1 and Ace1 transcriptional activators.

X-ray absorption spectroscopy on the minimal copper-regulatory domains of the two copper-regulated transcription factors (Ace1 and Mac1) in Saccharomyces cerevisiae revealed the presence of a remarkably similar polycopper cluster in both proteins. The Cu-regulatory switch motif of Mac1 consisting of the C-terminal first Cys-rich motif, designated the C1 domain, binds four Cu(I) ions as does the Cu-regulatory domain of Ace1. The four Cu(I) ions are bound to each molecule in trigonal geometry. An extended X-ray absorption fine structure (EXAFS) arising from outer-shell Cu...Cu interactions at 2.7 and 2.9 A was apparent in each Cu(I) complex indicative of a polycopper cluster. The intensity of the 2.9 A Cu...Cu backscatter peak, apparently diminished by partial cancellation, dominates the EXAFS. The results suggest that CuAce1 and CuMac1(C1) contain somewhat distorted forms of a known [Cu(4)-S(6)] cage in which a core of Cu atoms forming an approximate tetrahedron is bound by bridging thiolates above each of the six edges. The tetracopper clusters bound by Ace1 and Mac1 differ in that the Ace1 cluster is coordinated entirely by cysteinyl thiolate, whereas the cysteine-deficient Mac1 cluster appears to consist of a Cu(4)(S-Cys)(5)(N-His) cluster with a bridging histidyl-derived nitrogen.

Copper↗
PubMed2002

Biliary excretion of [(GS)(2)AsSe](-) after intravenous injection of rabbits with arsenite and selenate.

It has been shown that the seleno-bis (S-glutathionyl) arsinium ion, [(GS)(2)AsSe](-), is the major arsenic and selenium excretory product in bile of rabbits treated with arsenite and selenite [Gailer, J., Madden, S., Buttigieg, G. A., Denton, M. B., and Younis, H. S. (2002) Appl. Organomet. Chem. 16, 72-75]. To investigate the in vivo interaction between the other environmentally common oxy-anions of arsenic and selenium in mammals, we have intravenously injected rabbits with different combinations of the arsenic and selenium oxo-anions (arsenite + selenate, arsenate + selenite, and arsenate + selenate) and analyzed the collected bile and whole blood samples by X-ray absorption spectroscopy. Only the injection of arsenite and selenate led to the biliary excretion of [(GS)(2)AsSe](-) within 25 min. Whole blood collected from these animals (25 min postinjection) contained predominantly unchanged selenate, which suggests the presence of a mammalian selenate reductase in the liver. The lack of any significant biliary excretion of [(GS)(2)AsSe](-) in the other treatment groups implies that arsenate was not reduced in the liver on the time scale of our experiments. The relevance of these results for the human toxicology of arsenic and selenium is discussed.

Animals↗
PubMed2002

Selenium assimilation and volatilization from selenocyanate-treated Indian mustard and muskgrass.

Selenocyanate (SeCN(-)) is a major contaminant in the effluents from some oil refineries, power plants, and in mine drainage water. In this study, we determined the potential of Indian mustard (Brassica juncea) and muskgrass (a macroalga, Chara canescens) for SeCN(-) phytoremediation in upland and wetland situations, respectively. The tolerance of Indian mustard to toxic levels of SeCN(-) was similar to or higher than other toxic forms of Se. Indian mustard treated with 20 microM SeCN(-) removed 30% (w/v) of the Se supplied in 5 d, accumulating 554 and 86 microg of Se g(-1) dry weight in roots and shoots, respectively. Under similar conditions, muskgrass removed approximately 9% (w/v) of the Se supplied as SeCN(-) and accumulated 27 microg of Se g(-1) dry weight. A biochemical pathway for SeCN(-) degradation was proposed for Indian mustard. Indian mustard and muskgrass efficiently degraded SeCN(-) as none of the Se accumulated by either organism remained in this form. Indian mustard accumulated predominantly organic Se, whereas muskgrass contained Se mainly as selenite and organic Se forms. Indian mustard produced volatile Se from SeCN(-) in the form of less toxic dimethylselenide. Se volatilization by Indian mustard accounted for only 0.7% (w/v) of the SeCN(-) removed, likely because the biochemical steps in the production of dimethylselenide from organic Se were rate limiting. Indian mustard is promising for the phytoremediation of SeCN(-) -contaminated soil and water because of its remarkable abilities to phytoextract SeCN(-) and degrade all the accumulated SeCN(-) to other Se forms.

Biodegradation, Environmental↗