Abstract
Nitric oxide (NO.) is a naturally occurring toxin that some organisms adaptively resist. In aerobic or anaerobic Escherichia coli, low levels of NO. exposure inactivated the NO.-sensitive citric acid cycle enzyme aconitase, and inactivation was more effective when the adaptive synthesis of NO.-defensive proteins was blocked with chloramphenicol. Protection of aconitase in aerobically grown E. coli was dependent upon O2, was potently inhibited by cyanide, and was correlated with an induced rate of cellular NO. consumption. Constitutive and adaptive cellular NO. consumption in aerobic cells was also dependent upon O2 and inhibited by cyanide. Exposure of aerobic cells to NO. accordingly elevated the activity of the O2-dependent and cyanide-sensitive NO. dioxygenase (NOD). Anaerobic E. coli exposed to NO. or nitrate induced a modest O2-independent and cyanide-resistant NO.-metabolizing activity and a more robust O2-stimulated cyanide-sensitive activity. The latter activity was attributed to NOD. The results support a role for NOD in the aerobic detoxification of NO. and suggest functions for NOD and a cyanide-resistant NO. scavenging activity in anaerobic cells.
Highlights
Nitric oxide (NO1⁄7) is a naturally occurring toxin that some organisms adaptively resist
E. coli does not appear to produce a typical NOR activity, but it does produce a multiheme nitrite reductase with NO1⁄7-reducing capacity [19] and a nitric oxide dioxygenase (NOD) that has been proposed to function in NO1⁄7 detoxification [20]
480 ppm NO1⁄7 exerted no discernible effect on the anaerobic growth of E. coli in a minimal glucose medium supplemented with 10 mM nitrate
Summary
Nitric oxide (NO1⁄7) is a naturally occurring toxin that some organisms adaptively resist. Nitric oxide (NO1⁄7) is released by leukocytes and functions as an antibiotic [1,2,3] It may be produced endogenously by bacteria during the reduction of NO2Ϫ by nitrate reductase [4]. Tation of Escherichia coli to NO1⁄7 under the transcriptional control of the antioxidant regulators SoxRS and OxyR has been suggested, since these global antioxidant regulators provide some survival and growth benefits against NO1⁄7 [16, 17] or nitrosothiols [18], respectively It remains unclear how these regulators protect bacteria. E. coli does not appear to produce a typical NOR activity, but it does produce a multiheme nitrite reductase with NO1⁄7-reducing capacity [19] and a nitric oxide dioxygenase (NOD) that has been proposed to function in NO1⁄7 detoxification [20]
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