title: SP-22 is a thioredoxin-dependent peroxide reductase in mitochondria.
abstract: SP-22 is a mitochondrial antioxidant protein in bovine adrenal cortex. The protein is homologous to thioredoxin peroxidase and other antioxidant proteins. It protects radical-sensitive enzymes from oxidative damage by a radical-generating system (Fe2+/dithiothreitol) in the presence of a small amount of serum. In this study we purified a second mitochondrial protein with Mr 11,777, which cooperates with SP-22 to protect glutamine synthetase and other proteins from Fe2+/dithiothreitol-mediated damage. Without SP-22, the protein had no protecting activity. We determined amino acid and nucleotide sequences of the protein and its cDNA, respectively, and found that it was a protein of the thioredoxin family. The protein, designated as mt-Trx (mitochondrial thioredoxin), had a presequence composed of 59 amino acids that seemed to be a mitochondrial targeting signal. Mitochondrial extract prepared from adrenal cortex contained NADPH-dependent 5,5'dithiobis(2-nitrobenzoic acid) (Nbs2) reductase activity. The enzyme was thought to have thioredoxin reductase activity, since the Nbs2-reducing activity was stimulated by mt-Trx. We partially purified the Nbs2 reductase from bovine adrenocortical mitochondria. In the presence of the partially purified reductase, mt-Trx, and NADPH, SP-22 showed the activity to protect oxyhemoglobin against ascorbate-induced damage. Furthermore, with the three protein components (Nbs2 reductase, mt-Trx, and SP-22) NADPH was oxidized in the presence of hydrogen peroxide or tert-butyl hydroperoxide. The oxidation of NADPH was concomitant with the disappearance of an equimolar amount of hydrogen peroxide. Without any one of the protein components no hemoglobin-protecting and peroxide-dependent NADPH-oxidizing activities were observed. From these results we concluded that SP-22 is thioredoxin-dependent peroxide reductase or so-called thioredoxin peroxidase in mitochondria from the adrenal cortex.
authors.affiliation: Radioisotope Laboratory, Faculty of Agriculture, Yamaguchi University, Japan. watabe@agr.yamaguchi-u.ac.jp
authors.forename: S
authors.initials: S
authors.lastname: Watabe
authors.forename: T
authors.initials: T
authors.lastname: Hiroi
authors.forename: Y
authors.initials: Y
authors.lastname: Yamamoto
authors.forename: Y
authors.initials: Y
authors.lastname: Fujioka
authors.forename: H
authors.initials: H
authors.lastname: Hasegawa
authors.forename: N
authors.initials: N
authors.lastname: Yago
authors.forename: S Y
authors.initials: SY
authors.lastname: Takahashi
mesh_terms: D000302:Adrenal Cortex / Q000201:enzymology*; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002417:Cattle; D017931:DNA Primers / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D004579:Electron Transport; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D008928:Mitochondria / Q000201:enzymology* / Q000378:metabolism*; D008969:Molecular Sequence Data; D010108:Oxyhemoglobins / Q000378:metabolism; D010544:Peroxidases / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D061105:Peroxiredoxin III; D054464:Peroxiredoxins; D016133:Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid
chemical_list: D017931:DNA Primers; D018076:DNA, Complementary; D010108:Oxyhemoglobins; D010544:Peroxidases; C516115:PRDX3 protein, human; D061105:Peroxiredoxin III; D054464:Peroxiredoxins; D005974:Glutamate-Ammonia Ligase