Fig 1.

Analysis of FlRd expression in cells exposed to combined nitrosative and oxidative stress. (A) Immunoblotting analysis of E. coli K-12 cells grown anaerobically and exposed for 45 min to 50 μM NO and 3 mM H₂O₂, using antibodies against flavorubredoxin (FlRd) and flavohemoglobin (Hmp). (B and C) β-Galactosidase activities of E. coli RK4353 cells carrying plasmid pAA182-PnorV, which contains the norV promoter-lacZ fusion. Cells cultured anaerobically in LB were treated, at an OD₆₀₀ of 0.3, with 50 μM NO and/or 3 mM H₂O₂ (B) or with 25 μM spermine NONOate and/or 25 μM H₂O₂ (C). All cultures were subjected to the stresses for a total of 25 min. Sequential exposures were done by a 10-min exposure to H₂O₂ followed by a 15-min treatment with NO/NO donor and by exposure for 10 min to NO/NO donor followed by 15 min of treatment with H₂O₂. Results are means ± standard errors (SE) for three independent cultures assayed in duplicate. Activities are expressed in nmol of o-nitrophenol/min/mg of bacterial dry mass.