Figure 6.

Enhancement on tryptophan fluorescence on binding 60 μM AMPPNP to 2 μM S1dC: wt (blue trace); S236A mutant (black trace). Conditions were as in Figure 5. Fitting a biexponential to the data between 0.1 and 10 s yielded rate constants of 3.4 s⁻¹ (amplitude = 0.17) and 0.24 s⁻¹ (amplitude = 0.14) for the S236A construct. For the wild-type construct values were 5.4 s⁻¹ (amplitude = 0.085) and 0.92 s⁻¹ (amplitude = 0.081). The fluorescence signal was normalized to 1 for the apo state, so that the total fluorescence enhancement in these records was 31% for the S236A construct and 16.6% for the wild type.