Antioxidant vitamins C and E affect the superoxide-mediated induction of the soxRS regulon of Escherichia coli.
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).
Departamento de Microbiologa, LUSARAApartado Postal 102-006, 08930 Mxico, D. F.Mexico.
Ana M
AM
Fuentes
Departamento de Farmacologa, Facultad de MedicinaUNAM, 04510, Mxico, D. F.Mexico.|Departamento de Microbiologa, LUSARAApartado Postal 102-006, 08930 Mxico, D. F.Mexico.
Carlos F
CF
Amábile-Cuevas
D000975:Antioxidants / Q000378:metabolism / Q000494:pharmacology; D001205:Ascorbic Acid / Q000378:metabolism / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000187:drug effects* / Q000235:genetics / Q000502:physiology; D004926:Escherichia coli / Q000187:drug effects* / Q000235:genetics / Q000502:physiology; D029968:Escherichia coli Proteins; D005696:Galactosidases / Q000032:analysis; D005786:Gene Expression Regulation / Q000187:drug effects; D006540:Herbicides / Q000037:antagonists & inhibitors / Q000633:toxicity; D010084:Oxidation-Reduction; D010269:Paraquat / Q000037:antagonists & inhibitors / Q000633:toxicity; D018085:Regulon / Q000187:drug effects*; D015534:Trans-Activators; D014157:Transcription Factors / Q000187:drug effects* / Q000235:genetics / Q000502:physiology; D014810:Vitamin E / Q000378:metabolism / Q000494:pharmacology*; D014812:Vitamin K / Q000008:administration & dosage / Q000037:antagonists & inhibitors / Q000633:toxicity
D000975:Antioxidants; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D006540:Herbicides; D015534:Trans-Activators; D014157:Transcription Factors; D014812:Vitamin K; C070724:SoxR protein, Bacteria; C070725:SoxS protein, E coli; D014810:Vitamin E; D005696:Galactosidases; D010269:Paraquat; D001205:Ascorbic Acid