FIG. 3.

Time course of NarX autophosphorylation in the presence or absence of added nitrate or nitrite. (A to C) To initiate each set of NarX autophosphorylation reactions, 7 μl of a 10× ATP cocktail was added to 63 μl of diluted membranes which contained 10 mM (final concentration) KCl (A), 10 mM KNO₂ (B), or 1 mM KNO₃ (C). At the indicated time points, 9.5-μl aliquots were removed and mixed with 4 μl of gel loading buffer. The amount of protein applied per lane was 0.40 μg. All phosphorylation reactions were performed at 4°C. (D) Plot of NarX protein phosphorylation with time. Units of NarX-[³²P]phosphate are arbitrary units.