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Searches with the human Omega glutathione transferase (GST) identified two outlying groups of the GST superfamily in Arabidopsis thaliana which differed from all other plant GSTs by containing a cysteine in place of a serine at the active site. One group consisted of four genes, three of which encoded active glutathione-dependent dehydroascorbate reductases (DHARs). Two DHARs were predicted to be cytosolic, whereas the other contained a chloroplast targeting peptide. The DHARs were also active as thiol transferases but had no glutathione conjugating activity. Unlike most other GSTs, DHARs were monomeric. The other class of GST comprised two genes termed the Lambda GSTs (GSTLs). The recombinant GSTLs were also monomeric and had glutathione-dependent thiol transferase activity. One GSTL was cytosolic, whereas the other was chloroplast-targeted. When incubated with oxidized glutathione, the putative active site cysteine of the GSTLs and cytosolic DHARs formed mixed disulfides with glutathione, whereas the plastidic DHAR formed an intramolecular disulfide. DHAR S-glutathionylation was consistent with a proposed catalytic mechanism for dehydroascorbate reduction. Roles for the cytosolic DHARs and GSTLs as antioxidant enzymes were also inferred from the induction of the respective genes following exposure to chemicals and oxidative stress.

Original publication

DOI

10.1074/jbc.M202919200

Type

Journal article

Journal

J Biol Chem

Publication Date

23/08/2002

Volume

277

Pages

30859 - 30869

Keywords

Amino Acid Sequence, Arabidopsis, Catalysis, Cloning, Molecular, Glutathione Transferase, Homeostasis, Molecular Sequence Data, Oxidation-Reduction, Oxidoreductases