Selenite is a substrate for calf thymus thioredoxin reductase and thioredoxin and elicits a large non-stoichiometric oxidation of NADPH in the presence of oxygen

Eur J Biochem. 1992 Jul 15;207(2):435-39. doi: 10.1111/j.1432-1033.1992.tb17068.x.


The thioredoxin system, comprising NADPH, thioredoxin reductase and thioredoxin reduces protein disulfides via redox-active dithiols. We have discovered that sodium selenite is a substrate for the thioredoxin system; 10 microM selenite plus 0.05 microM calf thymus thioredoxin reductase at pH 7.5 caused a non-stoichiometric oxidation of NADPH (100 microM after 30 min). In contrast, thioredoxin reductase from Escherichia coli showed no direct reaction with selenite, but addition of 3 microM E. coli thioredoxin also resulted in non-stoichiometric oxidation of NADPH, consistent with oxidation of the two active-site thiol groups in thioredoxin to a disulfide. Kinetically, the reaction was complex with a lag phase at low selenite concentrations. Under anaerobic conditions the reaction stopped after 1 mol selenite had oxidized 3 mol NADPH; the admission of air then resulted in continued consumption of NADPH consistent with autooxidation of selenium intermediate(s). Ferricytochrome c was effectively reduced by calf thymus thioredoxin reductase and selenite in the presence of oxygen. Selenite caused a strong dose-dependent inhibition of the formation of thiol groups from insulin disulfides with either the E. coli or calf-thymus thioredoxin system. Thus, under aerobic conditions selenite catalyzed, NADPH-dependent redox cycling with oxygen, a large oxygen-dependent consumption of NADPH and oxidation of reduced thioredoxin inhibiting its disulfide-reductase activity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anaerobiosis
  • Animals
  • Cattle
  • Cytochrome c Group / metabolism
  • Disulfides / metabolism
  • Escherichia coli / enzymology
  • Insulin / metabolism
  • Kinetics
  • NADP / metabolism*
  • Oxidation-Reduction
  • Oxygen / metabolism
  • Selenium / metabolism*
  • Sodium Selenite
  • Thioredoxin-Disulfide Reductase / metabolism*
  • Thioredoxins / metabolism*
  • Thymus Gland / enzymology


  • Cytochrome c Group
  • Disulfides
  • Insulin
  • Thioredoxins
  • NADP
  • Thioredoxin-Disulfide Reductase
  • Selenium
  • Sodium Selenite
  • Oxygen