Fit of the overall ATPase rates of the gp44/62-gp45 complex to the sum
of the activities of species carrying one, two, three, and four bound
ATPs. A, measured ATPase rates obtained with 1 μm
gp44/62 in the presence of excess (10 μm) WT-gp45 (data points)
are plotted together with the fit (solid curve) of the data to
Equation 2 (see
“Experimental Procedures”). A Kd value of 27
μm was used for the binding of the ATP ligands, and the best fit
values (see “Experimental Procedures”) for the rates at which ATP
is hydrolyzed by complexes carrying one, two, three, and four bound ATP
molecules are 30.5 (±0.6) μm min-1, 24.1
(±0.5) μm min-1, 7.4 (±0.2)
μm min-1, and 2.87 (±0.3) μm
min-1, respectively. B, calculated fractions of the
different ATP-bound enzyme species in solution are plotted as a function of
ATP concentration. The enzyme binds four ATP molecules with a
Kd value of 27 μm. ES1,
ES2, ES3, and ES4
represent the concentrations of enzyme species with one, two, three, and four
ATPs bound, respectively, as a function of input ATP.