Abstract
Reactive oxygen species (ROS) such as superoxide radical, hydrogen peroxide and hydroxyl radical naturally occur during normal metabolism in the aerobic respiration. Ionizing radiation and redox-cycling agents are also the source of ROS. Under oxidative stress, organic macromolecules are oxidized by ROS, cause the cell death and mutation. Cells are equipped with multiple enzyme systems to defend against such oxidative stress.
Oxygen molecule produces superoxide radical by one electron reduction. Superoxide can be decompose to hydrogen peroxide, which in turn produces hydroxyl radical. It is interesting to know how cells respond to increased level of superoxide radical.
E. coli has superoxide dismutases such as SodA and SodB, and catalases such as KatE and KatG. SodA is induced by methyl viologen, which produces superoxide radical, while not SodB. The sodAsodB double mutant of E. coli is highly sensitive to methyl viologen. The induction of certain proteins by superoxide radical in E. coli is triggered by SoxRS proteins.
Superoxide-inducible (soi) genes were identified as LacZ fusion proteins in our laboratory. Some strains expressing Soi::LacZ fusion protein are sensitive to superoxide radical. The soi genes are under the control of SoxRS in E. coli. In this study, the soi genes were cloned and characterized to clarify the roles in defense against oxidative stress.
