Figure 5.

ATP substrate kinetics at differing ADP inhibitor concentrations for TaRca2-α and the ADP-insensitive K428R substitution. Activation velocities of TaRca2-α WT (A) and the K428R substitution (B) with varying concentrations of ADP inhibitor (I) added as indicated on the right of individual curves. A competitive-inhibition model fitted the data best (global R² > 0.98 for both variants) using the following equations: K_half-Obs = K_half^h(1 + I/K_i) and V = V_max × S^h/(K_half-Obs + S^h) where K_half is the ATP substrate corresponding to half-maximal velocity in μm, h is the Hill slope, S is the ATP substrate concentration, and I is the ADP inhibitor concentration in μm. The apparent inhibition binding constant (K_i) was determined to be 4.9 ± 1.5 μm for TaRca2-α and 3.4 ± 1.4 μm for K428R through iteration of the curves.