FIGURE 2.

Immediate and delayed phenotypes of superoxide stress in E. coli. A SOD⁻ mutant growing in anoxic medium was shifted at time 0 into oxic conditions. When Ile and Val were absent, growth stopped immediately due to the inactivation of dihydroxyacid dehydratase, a [4Fe-4S] enzyme. In contrast, growth continued for several hours in the aromatic-deficient medium. Enzyme analysis showed that mononuclear iron enzymes lost activity only slowly. At time 0 these enzymes were populated by ferrous iron; at 6 h they were populated by zinc. all AAs, all amino acids.