Figure 3. Consistency between theoretical and experimental isotope signal envelopes.

Comparisons of intensity ratios for neighboring isotope signals in an experimentally obtained envelope with the corresponding intensity ratios for a theoretical envelope assuming 98.2% ¹⁵N labeling efficiency. Left panel: theoretical isotope pattern for the peptide DVEGPEGFQTR from the aquaporin PIP2;2. Right panel: experimental isotope pattern for the same peptide. The difference from the theoretical ratio was calculated for each pair of signals and only isotopic envelopes that did not differ more than the threshold values preset in the settings file of the processing software were used for further analysis (calculations below the panel).