期刊
MARINE DRUGS
卷 11, 期 8, 页码 3025-3045出版社
MDPI AG
DOI: 10.3390/md11083025
关键词
microcystin; tryptophan oxidation; N-formylkynurenine; mass spectrometry; nuclear magnetic resonance spectroscopy; Microcystis CAWBG11
资金
- New Zealand Ministry of Business, Innovation and Employment [UOWX0505]
- Marsden Fund of the Royal Society of New Zealand [12-UOW-087]
- Research Council of Norway [196085/V10]
- University of Waikato Doctoral Scholarship
Microcystins are cyclic peptides produced by cyanobacteria, which can be harmful to humans and animals when ingested. Eight of the (more than) 90 microcystin variants presently characterized, contain the amino acid tryptophan. The well-researched oxidation products of tryptophan; kynurenine, oxindolylalanine, and N-formylkynurenine, have been previously identified in intact polypeptides but microcystin congeners containing oxidized tryptophan moieties have not been reported. Liquid chromatography-tandem mass spectrometric analysis of an extract of Microcystis CAWBG11 led to the tentative identification of two new tryptophan-containing microcystins (MC-WAba and MC-WL), as well as eight other microcystin analogs containing kynurenine, oxindolylalanine and N-formylkynurenine (Nfk). Investigation of one of these congeners (MC-NfkA) by nuclear magnetic resonance spectroscopy was used to verify the presence of Nfk in the microcystin. Liquid chromatography-mass spectrometry analysis of a tryptophan oxidation experiment demonstrated that tryptophan-containing microcystins could be converted into oxidized tryptophan analogs and that low levels of oxidized tryptophan congeners were present intracellularly in CAWBG11. MC-NfkR and MC-LNfk were detected in standards of MC-WR and MC-LW, indicating that care during storage of tryptophan-containing microcystins is required.
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