Figure 2.

(a) Overlay of the one-dimensional ¹H spectrum of aromatic region from ¹³C filtered and decoupled (lower, blue) and unfiltered ¹H spectrum (upper, black) of calcium-saturated calmodulin expressed during growth on [4-¹³C]-erythrose, deuterated pyruvate and D₂O indicating a selective introduction of a ¹H-¹³C pair at a single δ-carbon of Phe and Tyr. Also evident are resonances arising from hydrogen bonded to ¹²C at the ζ position of the aromatic ring of Phe (red arrows). These resonances have narrow line widths due to the absence of scalar coupling. A more detailed analysis of the ¹H spectrum is presented in the supplementary (Fig. S1 and S2). (b) The two-dimensional ¹³C-HSQC spectrum of the aromatic region and the corresponding one-dimensional ¹H spectrum (¹³C filtered) are shown. No significant ¹³C labeling of other amino acids was observed.