Mass Spectrometric Fragmentation Mechanism and Chromatographic Retention for Polypeptide Hormones-Systemins and Its Analogues

Fragmentation mechanism and chromatographic retention of systemins and systemin-like peptides were investigated by liquid chromatography online coupled to electrospray ionization-quadrupole time-of-flight mass spectrometry ( LC-ESI-QTOE-MS). The characteristic fragment ions of respective systemins, the rule of collision-induced dissociation (CID) as well as the chromatographic retention of these peptides on reversed phase LC were examined. The two to five fold protonated systemin ions were observed, and informative b-and y-type fragment ions were generated. The optimal collision energy of [M + 3H](3+) was found to be 22 V for tobacco systemin I (TobSys I), and [M + 4H](4+) was 18 V for respective tomato systemin (TomSys), potato systemin I (PotSys I) potato systemin II (PotSys), pepper systemin (PepSys) and nightshade systemin (NishSys), respectively. Under the optimal experimental conditions, abundant unique fragment ions of the systemins were generated, which can be used for the accurate qualitative and quantitative analysis of systemins. In addition, the results of chromatographic retention showed that the retention time of systemins was obviously influenced by trifluoroacetic acid (TFA) content in the sample solution.