HPLC purification of nisin(K12BocK) (red) produced in L. lactis and the corresponding control produced in the absence of BocK supplementation nisin(K12amber) (blue). (A) Comparing the elution chromatograms, the most interesting peak at 22 min is zoomed in (gray shading). Only if BocK was available in the growth medium, the highlighted peak was detectable. In contrast, no peak was visible for the control which lacks BocK supplementation (blue), indicating that no full-size peptide was synthesized. (B) MALDI–TOF–MS analysis of the samples above picture exemplary for all other measurements described in Table 1. For nisin(K12BocK), several different dehydration variants were detected. The most prominent signal at m/z = 5857.97 indicates a nisin variant with only four dehydrations. Depending on the location of the dehydrated serines and threonines, the formation of the first two or three rings is still possible, resulting in antimicrobial activity of the variants.