FIG 1.

Phosphoryl transfer from MBP-NarX₂₂₇ to His₆-NarL. Multiple-round assays were conducted in the presence of an ATP regeneration system. Note the different y axes, which result from the different amounts of phospho-NarX used to initiate the reactions. (A) NarL⁺. Reactions: ◆, NarX; ■, phospho-NarL⁺. This panel is redrawn from Fig. 3A in reference 13. (B) NarL V88A. Reactions: ◆, NarX; □, phospho-NarL V88A. This panel represents one of two independent experiments that yielded indistinguishable results.