Thermodynamics of the As(III)−Thiol Interaction:  Arsenite and Monomethylarsenite Complexes with Glutathione, Dihydrolipoic Acid, and Other Thiol Ligands

Colorimetric (near-UV absorption spectroscopy) and calorimetric (isothermal titration calorimetry) methods have been used to quantify the equilibrium and thermodynamics of arsenite and monomethylarsenite (MMA) coordinating to glutathione (GSH) and the dithiols dimercaptosuccinic acid (DMSA), dihydro...

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Bibliographic Details
Published in:Inorganic chemistry 2005-04, Vol.44 (8), p.2964-2972
Main Authors: Spuches, Anne M, Kruszyna, Harriet G, Rich, Anne M, Wilcox, Dean E
Format: Article
Language:English
Subjects:
Arsenates - chemistry
Arsenic - chemistry
Arsenic Poisoning
Arsenites - chemistry
Calorimetry
Cations
Dithiothreitol - chemistry
Glutathione - chemistry
Ligands
Organometallic Compounds - chemistry
Succimer - chemistry
Sulfhydryl Compounds - chemistry
Thermodynamics
Thioctic Acid - analogs & derivatives
Thioctic Acid - chemistry
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Summary:Colorimetric (near-UV absorption spectroscopy) and calorimetric (isothermal titration calorimetry) methods have been used to quantify the equilibrium and thermodynamics of arsenite and monomethylarsenite (MMA) coordinating to glutathione (GSH) and the dithiols dimercaptosuccinic acid (DMSA), dihydrolipoic acid (DHLA), and dithiothreitol (DTT). We found that both arsenite and MMA form moderately stable complexes (β = 106−107) with GSH; that arsenite forms a particularly stable 2:3 complex (β ≈ 1018) with the biological cofactor DHLA; that MMA has a somewhat higher affinity than arsenite for thiol ligands; and that entropic factors modulate the overall stability of As(III) complexes with thiols, which are favored by the exothermic formation of As(III)−thiolate bonds. The implications of these results for arsenic toxicity are discussed.
ISSN:0020-1669
1520-510X
DOI:10.1021/ic048694q