Low-energy collisionally activated decomposition and structural characterization of cyclic heptapeptide microcystins by electrospray ionization mass spectrometry
✍ Scribed by Yuan, Moucun; Namikoshi, Michio; Otsuki, Akira; Rinehart, Kenneth L.; Sivonen, Kaarina; Watanabe, Mariyo F.
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 209 KB
- Volume
- 34
- Category
- Article
- ISSN
- 1076-5174
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✦ Synopsis
Characteristics of electrospray ionization mass spectrometry/collision-induced dissociation (ESIMS/CID) mass spectra of microcystins, cyanobacterial cyclic heptapeptide hepatoxins, were examined. The collision conditions showed remarkable e †ects on the quality of the CID mass spectra, which were divided into three patterns according to the number of Arg residues. A characteristic cleavage reaction and neutral losses of MeOH, and NH 3 guanidine group(s) from the (2S,3S,8S,9S)-3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4E,6E-dienoic acid (Adda) and Arg residues were observed in the ESI and ESIMS/CID mass spectra, suggesting the most probable protonation sites in [ M + H ] ' and [ M + 2H ] 2' ions of microcystins. Microcystins with no Arg residue showed only [ M + H ] ' ions with a proton reacting at the methoxyl group in the Adda residue, and the ESIMS/CID/MS data revealed their structures unambiguously. The protonation site in [ M + H ] ' ions of microcystins with Arg residue(s) was the guanidine group. The [ M + 2H ] 2' ions of microcystins possessing one Arg residue had one proton on the Arg residue and probably another proton on the Adda residue, while the [ M + 2H ] 2' ions of microcystins having two Arg residues showed protonation at both Arg residues and the ESIMS/CID/MS data assigned their sequences. Structures of microcystins possessing one Arg residue can be assigned by ESIMS/CID/MS of [ M + H ] ' ions combined with those of [ M + 2H ] 2' ions.