Results of the ATP-PPi exchange assay to determine the substrate specificity of SyrE-A8 (A) Determination of kobs for three substrates: black diamonds, L-Asp, kobs = 6.3 min-1; gray squares, L-threo-3-OH-Asp, kobs = 0.2 min-1; white circles, L-erythro-3-OH-Asp, kobs = 0.1 min-1. (B) Comparison of % activation by SyrE-A8 of L-Asp, L-threo-3-OH-Asp, L-erythro-3-OH-Asp.