Fig 1.

Strip cross sections through the ¹⁵N planes of the 3D ¹⁵N–¹³C–¹³C chemical shift correlation spectrum of f-MLF-OH, showing the backbone resonance assignments. The Met ¹⁵N plane (125.5 ppm) shows only ¹³C cross-peaks from the Met residue. In contrast, the Leu ¹⁵N plane (116.2 ppm) shows Met and Leu ¹³C cross-peaks, and the Phe ¹⁵N plane (107.6 ppm) displays Leu and Phe ¹³C cross-peaks. Since ¹³C–¹³C correlations were established by using the SPC-5 double-quantum recoupling pulse sequence (31) the cross-peaks corresponding to subsequent ¹³C–¹³C dipolar transfers alternate in sign (28) (blue and red for positive and negative absorption, respectively). Details of the pulse sequence and experimental parameters used to record this spectrum can be found in ref. 22.