Constitutive and adaptive detoxification of nitric oxide in Escherichia coli -: Role of nitric-oxide dioxygenase in the protection of aconitase

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 O-2, 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 O-2 and inhibited by cyanide. Exposure of aerobic cells to NO. accordingly elevated the activity of the O-2-dependent and cyanide-sensitive NO. dioxygenase (NOD). Anaerobic E. coli exposed to NO. or nitrate induced a modest O-2-independent and cyanide-resistant NO.-metabolizing activity and a more robust O-2-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.