||P.444 right column bottom paragraph: "Only 0.1–1% of the electron flux through any particular enzyme is likely to be intercepted by O2. However, measurements of H2O2 efflux from scavenger-deficient cells indicate that the aggregate rate of H2O2 formation inside aerobic E. coli is 10–15 μM per second (Ref. 14). O2− formation is estimated to be about 5 μM per second, on the basis of in vitro studies [ref 22]. Because O2− and H2O2 react rapidly with vulnerable targets (see below), these rates are high enough to require the synthesis of ample scavenger enzymes (Box 2)."