title: Human monomethylarsonic acid (MMA(V)) reductase is a member of the glutathione-S-transferase superfamily.
abstract: The drinking of water containing large amounts of inorganic arsenic is a worldwide major public health problem because of arsenic carcinogenicity. Yet an understanding of the specific mechanism(s) of inorganic arsenic toxicity has been elusive. We have now partially purified the rate-limiting enzyme of inorganic arsenic metabolism, human liver MMA(V) reductase, using ion exchange, molecular exclusion, and hydroxyapatite chromatography. When SDS-beta-mercaptoethanol-PAGE was performed on the most purified fraction, seven protein bands were obtained. Each band was excised from the gel, sequenced by LC-MS/MS and identified according to the SWISS-PROT and TrEMBL Protein Sequence databases. Human liver MMA(V) reductase is 100% identical, over 92% of sequence that we analyzed, with the recently discovered human glutathione-S-transferase Omega class hGSTO 1-1. Recombinant human GSTO1-1 had MMA(V) reductase activity with K(m) and V(max) values comparable to those of human liver MMA(V) reductase. The partially purified human liver MMA(V) reductase had glutathione S-transferase (GST) activity. MMA(V) reductase activity was competitively inhibited by the GST substrate, 1-chloro 2,4-dinitrobenzene and also by the GST inhibitor, deoxycholate. Western blot analysis of the most purified human liver MMA(V) reductase showed one band when probed with hGSTO1-1 antiserum. We propose that MMA(V) reductase and hGSTO 1-1 are identical proteins.
authors.affiliation: Department of Molecular and Cellular Biology, Department of Pharmacology and Toxicology, Center of Toxicology, The University of Arizona, Tucson, AZ 85721, USA.
authors.forename: R A
authors.initials: RA
authors.lastname: Zakharyan
authors.forename: A
authors.initials: A
authors.lastname: Sampayo-Reyes
authors.forename: S M
authors.initials: SM
authors.lastname: Healy
authors.forename: G
authors.initials: G
authors.lastname: Tsaprailis
authors.forename: P G
authors.initials: PG
authors.lastname: Board
authors.forename: D C
authors.initials: DC
authors.lastname: Liebler
authors.forename: H V
authors.initials: HV
authors.lastname: Aposhian
mesh_terms: D000595:Amino Acid Sequence; D001151:Arsenic / Q000378:metabolism*; D001152:Arsenicals / Q000378:metabolism; D017886:Durapatite; D006801:Humans; D008099:Liver / Q000201:enzymology*; D013058:Mass Spectrometry; D008780:Methyltransferases / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction
chemical_list: D001152:Arsenicals; D017886:Durapatite; D008780:Methyltransferases; C020300:monomethylarsonic acid; D001151:Arsenic