Figure 4.

Average MS¹ [M + H]⁺ ion spectra of gramiketide A (A) and gramiketide B (B) each showing an overlay of the native ¹²C isotopolog pattern (orange) and ¹³C labeled isotopologs with a varying number of ¹²C tracer units incorporated (brown). Unrelated signals are shown in gray. Peak intensities were normalized to most abundant signals of ¹²C and ¹³C isotopologs, respectively.