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Low‐energy collisionally activated decomposition and structural characterization of cyclic heptapeptide microcystins by electrospray ionization mass spectrometry
Author(s) -
Yuan Moucun,
Namikoshi Michio,
Otsuki Akira,
Rinehart Kenneth L.,
Sivonen Kaarina,
Watanabe Mariyo F.
Publication year - 1999
Publication title -
journal of mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 1076-5174
DOI - 10.1002/(sici)1096-9888(199901)34:1<33::aid-jms754>3.0.co;2-l
Subject(s) - chemistry , protonation , mass spectrometry , residue (chemistry) , electrospray ionization , collision induced dissociation , mass spectrum , stereochemistry , electrospray , ion , tandem mass spectrometry , chromatography , organic chemistry
Characteristics of electrospray ionization massspectrometry/collision‐induced dissociation(ESIMS/CID) mass spectra of microcystins,cyanobacterial cyclic heptapeptide hepatoxins, were examined. Thecollision conditions showed remarkable effects on the quality of theCID mass spectra, which were divided into three patterns according tothe number of Arg residues. A characteristic cleavage reaction andneutral losses of MeOH, NH 3 and guanidinegroup(s) from the (2 S ,3 S ,8 S ,9 S )‐3‐amino‐9‐methoxy‐2,6,8‐trimethyl‐10‐phenyldeca‐4 E ,6 E ‐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. Copyright © 1999 John Wiley & Sons, Ltd.