ORIGINAL ARTICLESCharacterization of the monomethylarsonate reductase and dehydroascorbate reductase activities of Omega class glutathione transferase variants: implications for arsenic metabolism and the age-at-onset of Alzheimer's and Parkinson's diseasesSchmuck, Erica M.*; Board, Philip G.; Whitbread, Astrid K.; Tetlow, Natasha; Cavanaugh, Juleen A.; Blackburn, Anneke C.; Masoumi, AmirAuthor Information John Curtin School of Medical Research, Australian National University, Canberra, Australia Sponsorship: This work was supported by NHMRC grant 179818 to P.G.B. Correspondence and requests for reprints to Dr P. G. Board, Molecular Genetics Group, John Curtin School of Medical Research, PO Box 334 Canberra ACT 2601, Australia Tel: +61 2612 54714; fax: +61 2612 54712; e-mail: [email protected] Received 4 January 2005 Accepted 8 March 2005 *This work is published posthumously following the sudden death of Erica Schmuck on 25 August 2004. Pharmacogenetics and Genomics: July 2005 - Volume 15 - Issue 7 - p 493-501 doi: 10.1097/01.fpc.0000165725.81559.e3 Buy Metrics Abstract There are two functional Omega class glutathione transferase (GST) genes in humans. GSTO1 is polymorphic with several coding region alleles, including an A140D substitution, a potential deletion of E155 and an E208K substitution. GSTO2 is also polymorphic with an N142D substitution in the coding region. We investigated the effect of these variations on the enzyme's thioltransferase, dehydroascorbate reductase, monomethylarsonate reductase and dimethylarsonate reductase activities. Variant proteins were expressed in Escherichia coli and purified by Ni-agarose affinity chromatography. GSTO2-2 was insoluble and had to be dissolved and refolded from 8 M urea. The A140D and E208K substitutions in GSTO1-1 did not alter specific activity. The deletion of E155 caused a two- to three-fold increase in the specific activity with each substrate. This deletion also caused a significant decrease in the enzyme's heat stability. The E155 deletion has been linked to abnormal arsenic excretion patterns; however, the available data do not clearly identify the cause of this abnormality. We found that GSTO2-2 has activity with the same substrates as GSTO1-1, and the dehydroascorbate reductase activity of GSTO2-2 is approximately 70–100-fold higher than that of GSTO1-1. The polymorphic N142D substitution had no effect on the specific activity of the enzyme with any substrate. The most notable feature of GSTO2-2 was its very high dehydroascorbate reductase activity, which suggests that GSTO2-2 may significantly protect against oxidative stress by recycling ascorbate. A defect in ascorbate metabolism may provide a common mechanism by which the Omega class GSTs influence the age-at-onset of Alzheimer's and Parkinson's diseases. © 2005 Lippincott Williams & Wilkins, Inc.