FIG. 9.

Citrate-enhanced nonspecific cross-linking between TonB and FecA does not require energy derived from the PMF. Nonspecific FA-cross-linking experiments were prepared as described in the legend to Fig. 6. The experiments were performed in E. coli strain CO1031 carrying TonBC18ANP and either pBAD18 or pBADfecA (wild type [WT]). Following the resuspension of the cells in 10 mM sodium phosphate buffer (pH 6.8), 10 or 50 μm CCCP or 1 mM DNP was added either before or after the addition of 1 mM sodium citrate- 100 μm FeCl₃. The order in which various substrates or chemicals were added is indicated in ascending order by numbers 1 to 4 on the right. The leftmost lane is TonBC18ANP with pBAD18. TonB cross-linked with FecA is indicated. +, present; −, absent.