title: Identification of an enzymatically formed glutathione conjugate of the cyanobacterial hepatotoxin microcystin-LR: the first step of detoxication.
abstract: Cyanobacterial toxins have adverse effects on mammals, birds and fish and are being increasingly recognised as a potent stress factor and health hazard factor in aquatic ecosystems. Microcystins, cyclic heptapeptides and a main group of the cyanotoxins are mainly retained within the producer cells during cyanobacterial bloom development. However, these toxins are released into the surrounding medium by senescence and lysis of the blooms. Any toxin present could then come into contact with a wide range of aquatic organisms including phytoplankton grazers, invertebrates, fish and aquatic plants. Recent studies showed the conversion of microcystin in animal liver to a more polar compound in correlation with a depletion of the glutathione pool of the cell. The present study shows the existence of a microcystin-LR glutathione conjugate formed enzymatically via soluble glutathione S-transferase in various aquatic organisms ranging from plants (Ceratophyllum demersum), invertebrates (Dreissena polymorpha, Daphnia magna) up to fish eggs and fish (Danio rerio). The main derived conjugate was characterized by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry yielding a mass of m/z 1302, which is equivalent to the mass assumed for a glutathione microcystin-LR conjugate. This conjugate appears to be the first step in the detoxication of a cyanobacterial toxin in aquatic organisms.
authors.affiliation: Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 256, 12561 Berlin, Germany. pflug@igb-berlin.de
authors.forename: S
authors.initials: S
authors.lastname: Pflugmacher
authors.forename: C
authors.initials: C
authors.lastname: Wiegand
authors.forename: A
authors.initials: A
authors.lastname: Oberemm
authors.forename: K A
authors.initials: KA
authors.lastname: Beattie
authors.forename: E
authors.initials: E
authors.lastname: Krause
authors.forename: G A
authors.initials: GA
authors.lastname: Codd
authors.forename: C E
authors.initials: CE
authors.lastname: Steinberg
mesh_terms: D000818:Animals; D001427:Bacterial Toxins / Q000737:chemistry*; D001711:Biotransformation; D002851:Chromatography, High Pressure Liquid; D000458:Cyanobacteria / Q000378:metabolism*; D004137:Dinitrochlorobenzene / Q000378:metabolism; D005399:Fishes; D005978:Glutathione / Q000737:chemistry*; D005982:Glutathione Transferase / Q000378:metabolism; D008387:Marine Toxins; D013058:Mass Spectrometry; D052998:Microcystins; D010456:Peptides, Cyclic / Q000737:chemistry*; D014871:Water Microbiology
chemical_list: D001427:Bacterial Toxins; D004137:Dinitrochlorobenzene; D008387:Marine Toxins; D052998:Microcystins; D010456:Peptides, Cyclic; D005982:Glutathione Transferase; C057862:cyanoginosin LR; D005978:Glutathione