Fig. (5) Time course of inactivation of IleRS by ADP-PL.IleRS (6 µM) was incubated with 1 mM ADP-PL, as described under Methods. Kinetics of enzyme activity loss were superimposable for isoleucine-dependent isotopic [32P]PPi-ATP exchange and tRNAIle aminoacylation activities (● , ○ , ■). The control experiments (○) were without ADP-PL or with 1 mM ATP instead of ADP-PL. For the protection experiments (■), the enzyme was preincubated with 8 mM L-isoleucine and 8 mM ATP-Mg2+ prior to ADP-PL addition.