Tyr-dependent ATP hydrolysis by E. coli PheRS. Reactions were performed as described (15 μl samples) in the presence of 2 μM PheRS, with addition of tRNAPhe (2 μM) as indicated. Wild-type PheRS (▵), wild-type PheRS and tRNAPhe (▴), αA294G PheRS, (□), αA294G PheRS and tRNAPhe (▪). Inset, as main chart.