Interaction Of Arsenite Research Articles

Thermodynamic, kinetic and spectroscopic investigation of arsenite adsorption mechanism on pine cone-magnetite composite

Adsorptive removal of arsenite from wastewater often involves pre-oxidation to the less toxic arsenate followed by adsorption. Materials capable of simultaneous oxidation and adsorption could potentially improve the treatment of arsenic contaminated water. A novel magnetic composite consisting of Fenton’s treated pine cone, an agricultural waste and magnetite nanoparticles was prepared and applied to achieve simultaneous arsenite oxidation and adsorptive removal. A mechanistic investigation of the adsorption process was conducted to provide insights into the interaction of arsenite and the composite surface. X-ray diffraction peaks of the nanoparticles matched those of synthetic magnetite and X-ray photoelectron spectroscopy (XPS) indicated that Fe2+/Fe3+ ratio was in accordance with that of magnetite at 0.5. Arsenite removal efficiency by the as-synthesised composite was approximately 90% with a maximum adsorption capacity of 17 mg g−1. Kinetic studies revealed that arsenic adsorption was a multi-step process with surface adsorption and intra-particle diffusion contributing to the rate limiting step. Ion exchange was evident from the release of pre-loaded nitrate ions during arsenite adsorption. Spectroscopic evidence confirmed ion exchange through the observance of hydroxyl peak shift, reduction in intensity of carboxylate peaks and AsOFe bond formation during adsorption. Further, XPS results confirmed that there was simultaneous reduction of Fe3+ to Fe2+, oxidation of arsenite to arsenate and adsorption of both arsenite and arsenate on the composite surface through the formation of inner sphere complexes.

Interaction of arsenite with a zinc finger CCHC peptide: Evidence for formation of an As–Zn-peptide mixed complex

The interaction of arsenite with a Cys 3His (CCHC) zinc finger model (34–51) HIV-1 nucleocapsid protein p7 (NCp7) peptide in the absence and presence of Zn II was studied using fluorescence spectroscopy, CD (circular dichroism) and ESI-MS (Electrospray Ionization Mass Spectrometry). We found that arsenic forms different complexes with the free peptide and the zinc finger peptide. In the former case the peptide conformation differed greatly from that of the zinc finger, whereas in the second case a mixed As–Zn-peptide complex was formed with partial preservation of zinc finger conformation. An apparent stability constant was estimated for the mixed As–Zn-peptide complex ( K = 2083 M − 1 and 442 M − 1 at 25 °C and pHs 6 and 7, respectively). Our study also shows that the interaction of arsenic with the CCHC motif is facilitated by glutathione (GSH), through formation of a GS–As-peptide conjugate.

Inhibition of Poly(ADP-ribose) Polymerase-1 by Arsenite Interferes with Repair of Oxidative DNA Damage

Arsenic enhances skin tumor formation when combined with other carcinogens, including UV radiation (UVR). In this study we report that low micromolar concentrations of arsenite synergistically increases UVR-induced oxidative DNA damage in human keratinocytes as detected by 8-hydroxyl-2'-deoxyguanine (8-OHdG) formation. Poly(ADP-ribose) polymerase-1 (PARP-1) is involved in base excision repair, a process that repairs 8-OHdG lesions. Arsenite suppresses UVR-induced PARP-1 activation in a concentration-dependent manner. Inhibition of PARP-1 activity by 3-aminobenzamide or small interfering RNA silencing of PARP-1 expression significantly increases UVR-induced 8-OHdG formation, suggesting that inhibition of PARP-1 activity by arsenite contributes to oxidative DNA damage. PARP-1 is a zinc finger protein, and mass spectrometry analysis reveals that arsenite can occupy a synthetic apopeptide representing the first zinc finger of PARP-1 (PARPzf). When the PARPzf peptide is preincubated with Zn(II) followed by incubation with increasing concentrations of arsenite, the ZnPARPzf signal is decreased while the AsPARPzf signal intensity is increased as a function of arsenite dose, suggesting a competition between zinc and arsenite for the same binding site. Addition of Zn(II) abolished arsenite enhancement of UVR-stimulated 8-OHdG generation and restored PARP-1 activity. Our findings demonstrate that arsenite inhibits oxidative DNA damage repair and suggest that interaction of arsenite with the PARP-1 zinc finger domain contributes to the inhibition of PARP-1 activity by arsenite. Arsenite inhibition of poly(ADP-ribosyl)ation is one likely mechanism for the reported co-carcinogenic activities of arsenic in UVR-induced skin carcinogenesis.

Effects of arsenite on estrogen receptor-alpha expression and activity in MCF-7 breast cancer cells.

To determine whether arsenite has estrogen-like activities, the effects of this compound on estrogen receptor-alpha (ERalpha) and other estrogen-regulated genes were measured in the human breast cancer cell line MCF-7. Treatment of cells with 1 microM arsenite resulted in a 60% decrease in the amount of ERalpha and in a parallel decrease of 40% in ERalpha messenger RNA. Progesterone receptor concentration increased 22-fold after arsenite treatment. pS2 messenger RNA also increased 2. 1-fold after treatment. The induction of progesterone receptor and pS2 was blocked by the antiestrogen ICI-182,780. In transient cotransfection experiments of wild-type ERalpha and an estrogen response element-reporter construct, arsenite stimulated chloramphenicol acetyltransferase (CAT) activity. In growth assays, arsenite significantly stimulated the proliferation of MCF-7 cells compared with cells grown in estrogen-depleted medium. Addition of an antiestrogen blocked growth stimulation by arsenite. In binding assays, arsenite blocked the binding of estradiol to ERalpha (Ki = 5 +/- 0.5 nM; n = 3), suggesting that the compound interacts with the hormone-binding domain of the receptor. To determine whether interaction of arsenite with the hormone-binding domain results in receptor activation, COS-1 cells were transiently cotransfected with the chimeric receptors GAL-ER, which contains the hormone-binding domain of ERalpha and the DNA-binding domain of the transcription factor GAL4, and a GAL4-responsive CAT reporter gene. Treatment of cells with estradiol or arsenite resulted in a 4-fold increase in CAT activity. The effects of arsenite on the chimeric receptor were blocked by the antiestrogen, suggesting that arsenite activates ERalpha through an interaction with the hormone-binding domain of the receptor. Transfection assays with ERalpha mutants identified C381, C447, H524, and N532 as interaction sites of arsenite with the hormone-binding domain.

The Interaction of Arsenite with the Molybdenum Center of Chicken Liver Xanthine Dehydrogenase

Inactivation of chicken liver xanthine dehydrogenase by arsenite is reflected in the molybdenum electron paramagnetic resonance signal at g = 1.97. The arsenite spectrum shows additional splittings and considerable broadening yet remains comparable to the native in total intensity. Further subtle alterations of the molybdenum signal of arsenite-treated enzyme are seen in the presence of purine-type substrates or inhibitors.

The mechanism of arsenate inhibition of the glucose active transport system in Neurospora crassa

The mechanism of arsenate inhibition of the glucose active transport system in wild-type cells of Neurospora crassa has been examined. Arsenate treatment results in approximately 65% inhibition of the glucose active transport system with only a small depression of cellular ATP levels. The transport system is not inhibited in cells treated with sodium arsenate in the presence of sodium azide. The transport inhibition is suppressed when orthophosphate is present during arsenate treatment, but is not reversed by orthophosphate when added after the arsenate treatment. The transport inhibition is completely reversed by treatment of the cells with mercaptoethanol. Gel chromatography of sonicates of intact cells which had been treated with [ 74As]arsenate reveals three radioactive peaks, one with the elution volume of arsenate, one with the elution volume of arsenite, and a high molecular-weight radioactive fraction. Treatment of the high molecular-weight radioactive fraction with mercaptoethanol results in the production of radioactive arsenite. In view of these findings, it is proposed that arsenate inhibition of the glucose active transport system in Neurospora involves transport of arsenate into the cells, probably via the orthophosphate transport system, reduction of the transported arsenate to arsenite, and interaction of arsenite with some component of the glucose active transport system, presumably via covalent binding with vicinal thiol groups.