Fig 2.

[⁵⁵Fe]ferrichrome transport supported by ExbB TMD substitutions. ExbB TMD substituted mutants were expressed at chromosomal levels in strain RA1017 (ΔexbBD ΔtolQRA), and the initial rates of [⁵⁵Fe]ferrichrome transport were measured as described in Materials and Methods. Triplicate samples were taken at all time points, and the initial transport rates were calculated by linear regression. Linear regression slopes were normalized to plasmid-encoded wild-type ExbBD (pExbBD) (100%). Normalized percent activities of at least two independent experiments were averaged, and standard deviations are indicated by the error bars. ExbB TMD substitutions are presented as follows: (A) substitution of hydroxyl residues; (B) substitution of proline, charged, and the remaining polar residues; (C) substitution of glycine residues.