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Cyclic peptide hepatotoxins from freshwater cyanobacterial (blue‐green algae) waterblooms collected in Central China
Author(s) -
Zhang QingXue,
Yu MinJuan,
Li ShangHao,
Carmichael Wayne W.
Publication year - 1991
Publication title -
environmental toxicology and chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.1
H-Index - 171
eISSN - 1552-8618
pISSN - 0730-7268
DOI - 10.1002/etc.5620100303
Subject(s) - toxin , microcystis aeruginosa , cyanobacteria , microcystin , oscillatoria , hepatotoxin , bioassay , microbiology and biotechnology , marine toxin , biology , cyanotoxin , amino acid , microcystis , biochemistry , peptide , anabaena , microcystin lr , chemistry , bacteria , toxicity , genetics , organic chemistry
Toxic cyanobacteria (blue‐green algae) waterblooms have been found in several Chinese water bodies since studies began there in 1984. Waterbloom samples for this study contained Anabaena circinalis, Microcystis aeruginosa and Oscillatoria sp. Only those waterblooms dominated by Microcystis aeruginosa were toxic by the intraperitoneal (i.p.) mouse bioassay. Signs of poisoning were the same as with known hepatotoxic cyclic peptide microcystins. One toxic fraction was isolated from each Microcystis aeruginosa sample. Two hepatotoxic peptides were purified from each of the fractions by high‐performance liquid chromatography and identified by amino acid analysis followed by low and high resolution fast‐atom bombardment mass spectrometry (FAB‐MS). LD50 i.p. mouse values for the two toxins were 245 μg/kg (Toxin A) and 53 μg/g (Toxin B). Toxin content in the cells was 0.03 to 3.95 mg/g (Toxin A) and 0.18 to 3.33 mg/kg (Toxin B). The amino acid composition of Toxin A was alanine [1], arginine [2], glutamic acid [1] and β‐methylaspartic acid [1]; for Toxin B it was the same, except one of the arginines was replaced with a leucine. Low‐ and high‐resolution FAB‐MS showed that the molecular weights were 1,037 m/z (Toxin A) and 994 m/z (Toxin B), with formulas of C 49 H 76 O 12 N 13 (Toxin A) and C 49 H 75 O 12 N 10 (Toxin B). It was concluded that Toxin A is microcystin‐RR and Toxin B is microcystin‐LR, both known cyclic heptapeptide hepatotoxins isolated from cyanobacteria in other parts of the world. Sodium borohydride reduction of microcystin‐RR yielded dihydro‐microcystin‐RR (m/z = 1,039), an important intermediate in the preparation of tritium‐labeled toxin for metabolism and fate studies.