Figure 2.

(A) Expansion of the region of the broadband spectrum of an RPLC fraction (29 min) containing the 12⁺ charge state of the CNBr digestion peptide of apo PheATE. Also present is the 11⁺ charge state of a peptide from PheATE that does not contain the active site (Leu¹⁴⁰–Met²⁴³). (Inset) Expansion of isotopic distribution for the 12,611.0 Da component. (B) Spectrum containing the 12⁺ charge state of the holo form of the PheATE CNBr digestion peptide. (C) Region of the spectrum containing the 12⁺ charge state from material treated with a 1:1 mixture of d₀- and d₅-Phe before digestion. (Inset) Expansion of isotopic distribution for the 13,097.4 Da component. Open squares indicate the theoretical distribution for d₀-Phe loaded peptide; open triangles, the d₅-Phe loaded peptide. The actual ratio determined for the loading of d₀- to d₅-Phe was 53%:47%, for which the theoretical distribution is represented by the solid circles. An * indicates an adduct peak.