Figure 1.

INADEQUATE of 200 mM natural abundance (A) and 2 mM 99% ¹³C-labeled histidine (B). This experiment provides direct one bond ¹³C-¹³C coupling information that allows the molecular backbone of histidine to be traced (A). Fully isotopically labeled compounds give significantly increased signal to noise but also results in additional coherences (resonances not circled) beyond the typical double quantum that are essentially artifacts of multiple interacting spin systems (B). Peaks in (B) that are not in the drawn network are extra coherences not seen at natural abundance.