A comparison of the fluorescence decay for three conditions is shown: (1) incubation in 125μM mantATP chased by 4mM ATP (red); (2) incubation in 125μM mantADP chased by 4mM ADP (blue); (3) incubation in 125μM mantATP and 4 mM ATP chased by 4mM ATP (green). The experiment for 125μM mantATP chased by 4mM ATP was recorded and fit out to 3000s. Only the initial 800s are shown to facilitate comparison with the other two conditions. Parameters of the fits: (1) P1=0.42, T1=15s, P2=0.15, T2=221s, P3=0.40, T3=1730; (2) P1=0.55, T1=6s, P2=0.26, T2=21.4s, P3=0.10, T3=164s; (3) P1=0.77, T1=12.4s, P3=0.15, T3=63s. Data for case (2) were well fit (χ2 = 0.000015) using only a two-exponential fit. Only for case (1) is there a significant SRX component (P3) to the fluorescence decay.