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Mar. Drugs 2013, 11(8), 3025-3045; doi:10.3390/md11083025
Article

Structural Characterization of New Microcystins Containing Tryptophan and Oxidized Tryptophan Residues

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Received: 8 June 2013; in revised form: 15 July 2013 / Accepted: 15 July 2013 / Published: 21 August 2013
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Abstract: 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.
Keywords: microcystin; tryptophan oxidation; N‑formylkynurenine; mass spectrometry; nuclear magnetic resonance spectroscopy; Microcystis CAWBG11 microcystin; tryptophan oxidation; N‑formylkynurenine; mass spectrometry; nuclear magnetic resonance spectroscopy; Microcystis CAWBG11
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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MDPI and ACS Style

Puddick, J.; Prinsep, M.R.; Wood, S.A.; Miles, C.O.; Rise, F.; Cary, S.C.; Hamilton, D.P.; Wilkins, A.L. Structural Characterization of New Microcystins Containing Tryptophan and Oxidized Tryptophan Residues. Mar. Drugs 2013, 11, 3025-3045.

AMA Style

Puddick J, Prinsep MR, Wood SA, Miles CO, Rise F, Cary SC, Hamilton DP, Wilkins AL. Structural Characterization of New Microcystins Containing Tryptophan and Oxidized Tryptophan Residues. Marine Drugs. 2013; 11(8):3025-3045.

Chicago/Turabian Style

Puddick, Jonathan; Prinsep, Michèle R.; Wood, Susanna A.; Miles, Christopher O.; Rise, Frode; Cary, Stephen C.; Hamilton, David P.; Wilkins, Alistair L. 2013. "Structural Characterization of New Microcystins Containing Tryptophan and Oxidized Tryptophan Residues." Mar. Drugs 11, no. 8: 3025-3045.


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