FIGURE 5.

Time course of the monomer/dimer equilibration following ATP hydrolysis. A, effects of ATP and MgATP on MJ (red) and MJI (black) Trp-174 fluorescence. The first (black) and second (red) Mg-labeled arrows indicate the addition of MgCl₂ to MJI and MJ, respectively. The final concentrations of MJ or MJI, ATP, and Mg were 2 μm, 2 mm, and 10 mm, respectively. B, time course of the Trp-174 fluorescence increase elicited by MgATP after rapid mixing. MJ incubated with 2 mm ATP was mixed on a stop-flow apparatus with an equal volume of buffer containing MgATP, and the changes in Trp fluorescence were followed. The final concentrations of MJ, ATP, and Mg were 2 μm, 2 mm, and 10 mm, respectively. The black line is a single-exponential fit to the data. C, response of MJ Trp-174 fluorescence to low [MgATP]. MJ was exposed to 10 mm Mg and then 5 μm ATP followed by 2 mm ATP. The concentrations of MJ and MJI in all panels were 2 μm, and the records are representative of data from at least four similar experiments.