FIGURE 2.

Calcium activation and GTP inhibition of wt and mutant TG2 activity. A, the transamidating activity of TG2 (13 nm) was assayed at increasing Ca²⁺ concentrations (10, 25, 50, 100, 250, 500, 1000, 2500, 5000 μm) as described under “Experimental Procedures.” B, TG transamidation was assayed at increasing concentrations of GTP (10, 50, 100, 200, 500, 1000, 2000 μm) in the presence of 150 μm Ca ²⁺. Data are expressed as a percentage of the maximal TG activity for each protein and are presented as the mean ± S.E. of five (A) and three (B) independent experiments carried out in triplicate. Sigmoid curves were fitted to “sigmoid dose-response (variable slope)” using GraphPad Prism. R² was ≥ 0.93.