Toxic peptides from freshwater cyanobacteria (blue-green algae). I. Isolation, purification and characterization of peptides from Microcystis aeruginosa and Anabaena flos-aquae

Abstract

Toxic peptides from two European Microcystis aeruginosa and one Canadian Anabaena flos-aquae species of freshwater cyanobacteria (blue-green algae) were purified by high performance liquid chromatography (HPLC) and examined by amino acid analysis and mass spectrometry. A toxic fraction from a butanol/methanol extract of toxic lyophilized cells was separated by G-25 gel filtration and purified by HPLC using a C-18 semi-preparative Column. A toxic peak with the same elution time was detected for each of the three toxic cyanobacteria. The desalted purified toxins (i.p. LD50 in mice, 50 micrograms/kg) caused signs of poisoning identical with previous literature reports of hepatotoxic peptides from Microcystis. On hydrolysis and amino acid analysis all three toxins showed a similar profile, consisting of equimolar amounts of glutamic acid, alanine, arginine and leucine. beta-methyl aspartic acid was identified in all of the toxic peptides. The fast atom bombardment mass spectra of the toxins indicated the molecular weight to be 994 for all the peptides. The absence of sequence ions in their corresponding fast atom bombardment mass spectra indicated the peptides to be cyclic.