FIG. 4.

Effects of unlabeled ATP on the accumulation of radiolabeled MBP-NarX₁₈₅ and MBP-NarQ₁₈₂ with the addition of an ATP-regenerating system (B and D) or without (A and C) in 30 nM [γ-³²P]ATP (MBP-NarX₁₈₅, 5,600 cpm fmol⁻¹, and MBP-NarQ₁₈₂, 5,000 cpm fmol⁻¹). At the time points shown, 5-μl samples of radiolabeled protein were quantified as described in Materials and Methods. Specific levels of phosphorylation are expressed as pmol of incorporated ³²P per total amount of protein used, expressed as μmol. Immediately following the removal of the 4-min sample, different concentrations of unlabeled ATP were added to the reaction mixtures (arrows) with the following final concentrations: 1× standard buffer (solid squares), 10 μM ATP (diamonds), 100 μM ATP (triangles), and 1,000 μM ATP (open squares). (A and B) MBP-NarX₁₈₅. (C and D) MBP-NarQ₁₈₂. The data represent one of two independent measurements.