FIG 3 .

IlvE proteins are modified by 2AA. IlvE protein samples were subjected to the relevant treatment prior to MS analysis as described in Materials and Methods. (A) Untreated; (B) incubated with 3CA; (C) untreated; (D) incubated with IlvA/serine; (E) IlvE purified from the ridA⁺ strain; (F) IlvE purified from a ridA strain. Samples in panels A, B, E, and F were precipitated with acetone and resuspended in acid before mass spectral analysis, while samples in panels C and D were separated by LC before mass analysis. In samples A, C, and E, no species with an additional 317 amu was visible.