Figure 2.

Effect of cysteine-scanning mutagenesis on IIA^Glc binding. Lac permease residues from Region I (A) and Region II (B) (Fig. 1) were mutated to cysteine. The percent of IIA^Glc bound to the various cysteine mutants compared with the Cys-less lac permease control was determined (■); for some of the residues, the single-cysteine residues were modified with NEM before the binding assays (□). ○, the previously determined initial rates of [¹⁴C]-lactose transport as percent of the Cys-less control (20–22). The average rate for Cys-less lac permease was 55 nmol⋅min⁻¹⋅(mg of protein)⁻¹.