Antioxidant vitamins C and E affect the superoxide-mediated induction of the soxRS regulon of Escherichia coli

Microbiology (Reading). 1998 Jul:144 ( Pt 7):1731-1736. doi: 10.1099/00221287-144-7-1731.


The mechanism of activation of Escherichia coli redox sensory protein SoxR is still unclear: a [2Fe-2S] cluster contained in a SoxR dimer is potentially redox-sensitive, but the nature of the signal is unknown. Antioxidant vitamins C (ascorbate) and E (alpha-tocopherol) were used to explore the mechanism of activation of the SoxR protein in vivo. Treating E. coli cells with ascorbate or alpha-tocopherol increased their tolerance to paraquat (PQ, a redox-cycling compound), even in the absence of the soxRS locus, suggesting a radical-quenching activity. When using a soxS'::lacZ fusion, whose expression is governed by activated SoxR, ascorbate and alpha-tocopherol also prevented the expression of beta-galactosidase after PQ treatment. A secondary activity was observed in cells carrying soxR101, a mutation resulting in the constitutive expression of the sox regulon, where the overexpression of soxS'::lacZ was also reduced by ascorbate or alpha-tocopherol treatment. Additionally, different mechanisms of action were revealed as alpha-tocopherol was capable of preventing both PQ and meanadione (MD) lethality, whilst ascorbate prevented PQ lethality but increased MD-mediated cell death. It is proposed that alpha-tocopherol, positioned in membranes, can prevent superoxide-dependent membrane damage; however, water-soluble ascorbate is unable to do so and can even increase the concentration of oxygen radicals reacting with released membrane-associated Fe(II).

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antioxidants / metabolism
  • Antioxidants / pharmacology
  • Ascorbic Acid / metabolism
  • Ascorbic Acid / pharmacology*
  • Bacterial Proteins / drug effects*
  • Bacterial Proteins / genetics
  • Bacterial Proteins / physiology
  • Escherichia coli / drug effects*
  • Escherichia coli / genetics
  • Escherichia coli / physiology
  • Escherichia coli Proteins*
  • Galactosidases / analysis
  • Gene Expression Regulation / drug effects
  • Herbicides / antagonists & inhibitors
  • Herbicides / toxicity
  • Oxidation-Reduction
  • Paraquat / antagonists & inhibitors
  • Paraquat / toxicity
  • Regulon / drug effects*
  • Trans-Activators*
  • Transcription Factors / drug effects*
  • Transcription Factors / genetics
  • Transcription Factors / physiology
  • Vitamin E / metabolism
  • Vitamin E / pharmacology*
  • Vitamin K / administration & dosage
  • Vitamin K / antagonists & inhibitors
  • Vitamin K / toxicity


  • Antioxidants
  • Bacterial Proteins
  • Escherichia coli Proteins
  • Herbicides
  • Trans-Activators
  • Transcription Factors
  • Vitamin K
  • SoxR protein, Bacteria
  • SoxS protein, E coli
  • Vitamin E
  • Galactosidases
  • Paraquat
  • Ascorbic Acid