FIG 7.

Iron internalization by TbpB-deficient strains. Whole, iron-stressed, TbpB-deficient gonococcal cells were applied to microtiter dishes for radiolabeled iron uptake assays. Iron uptake was calculated as counts per microgram of protein. Specific uptake was calculated by subtracting the counts obtained with KCN from those generated from metabolically active cells. Specifically internalized iron counts were then normalized to that of FA6905 (WT TbpA). FA6905 served as the positive control, and FA6905 L3HA (L3HA) and the excess competitor hTf condition (Comp) served as negative controls. The data represent the means ± standard errors of at least three independent binding experiments. For all of the mutants compared to the positive control, the P values were <0.001. Statistics were calculated with the Student t test.