SP-22 is a thioredoxin-dependent peroxide reductase in mitochondria

Eur J Biochem. 1997 Oct 1;249(1):52-60. doi: 10.1111/j.1432-1033.1997.t01-1-00052.x.

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.

Publication types

  • Comparative Study

MeSH terms

  • Adrenal Cortex / enzymology*
  • Amino Acid Sequence
  • Animals
  • Base Sequence
  • Cattle
  • DNA Primers / genetics
  • DNA, Complementary / genetics
  • Electron Transport
  • Glutamate-Ammonia Ligase / metabolism
  • Humans
  • In Vitro Techniques
  • Mitochondria / enzymology*
  • Mitochondria / metabolism*
  • Molecular Sequence Data
  • Oxyhemoglobins / metabolism
  • Peroxidases / genetics
  • Peroxidases / isolation & purification
  • Peroxidases / metabolism*
  • Peroxiredoxin III
  • Peroxiredoxins
  • Polymerase Chain Reaction
  • Sequence Homology, Amino Acid

Substances

  • DNA Primers
  • DNA, Complementary
  • Oxyhemoglobins
  • Peroxidases
  • PRDX3 protein, human
  • Peroxiredoxin III
  • Peroxiredoxins
  • Glutamate-Ammonia Ligase

Associated data

  • GENBANK/D87741