ATP-induced dissociation of the MT-HFG380B2 complex. (A) Representative time courses of the ATP-induced dissociation of the MT-HFG380B2 complex (1 μM MT and 0.2 μM HFG380B2) after mixing with 10, 50, and 250 μM ATP (jagged black curves). The smooth red curves are fits to double exponentials with rate constants of 23 s−1 and 3.4 s−1 (10 μM ATP), 78 s−1 and 12 s−1 (50 μM ATP), and 230 s−1 and 27 s−1 (250 μM ATP). (B) The observed rates (left scale) of the fast (filled red squares) and slow (open blue squares) phases of the ATP-induced dissociation as a function of ATP concentration. The rates of the fast phase were fitted to a hyperbola (red curve), giving kdis and K values of 310 s−1 and 7.5 × 103 M−1, respectively. The rates of the slow phase also were fitted to a hyperbola (blue curve) with the extrapolated maximum rate of 31 s−1. The gray line plots the percentage of the fast-phase amplitude against the total amplitude (right scale) in the double-exponential fitting. Error bars represent standard deviations.