FIG. 3.

Determination of differentially expressed peptide peak areas. The peak at m/z 579.31, corresponding to the constitutively expressed tryptic peptide AQAAEIVEQAK from the P. aeruginosa ATP synthase β-subunit, was observed at approximately the same level in each of the four analyses (anaerobic [A and B] and aerobic [C and D]). Since the peak areas varied maximally by a factor of 4, a 10-fold change in area was used in the subsequent determination of differentially expressed m/z values. The peak shown at m/z 488.77 represents one such differentially expressed peptide m/z ratio. Note the consistency of the chromatographic elution profiles that easily permits alignment of the proper peaks.