FIGURE 2.

ITC analysis of nucleotide binding to AtAPSK. A, titration of AtAPSK with ATP (solid squares), ATPγS (open squares), AMP-PNP (closed circles), and AMP-PNP + 5 mm Mg²⁺ (open circles). B, titration of AtAPSK with ADP (open squares) and ADP + 5 mm Mg²⁺ (solid squares). C, titration of AtAPSK with APS (open squares) and APS + 5 mm Mg²⁺ (solid squares). Representative experimental data for the ATP (A), ADP (B), and APS (C) titrations are plotted as heat signal (μcal s⁻¹) versus time (min) in each upper panel. Each experiment consisted of 20 to 30 injections of 10 μl each of nucleotide into a solution containing AtAPSK dimer. Each lower panel shows the integrated heat responses per injection. The solid line is the linear regression fit using a two-site binding model (see Table 2).