Characterization of heptapeptide toxins extracted from Microcystis aeruginosa (Egyptian isolate)

Four toxic peptides from local fresh water cyanobacterium Microcystis aeruginosa were purified and identified by high performance liquid chromatography (HPLC) and ion spray mass spectroscopic studies as: RR; YR; LR and LA with molecular weights of 1006.8, 1073, 984.8 and 910.6 respectively. Amino acid analysis indicated the presence of equimolar amounts of aspartic acid, glutamic acid, arginine, leucine and tyrosine, in addition to both alanine and dehydroalanine. Mouse assay toxicity indicated that the first two peptides, at the peak area of RR, YR. were highly toxic with LD₅₀ 20, 18.2 μg/kg body weight; however, the latter two, at the peak areas LR and I.A. have a lesser toxicity with LD₅₀ 36 and 40 μg/kg body weight respectively. Three linear peptide analogs to those naturally found devoid of Adda were synthesized using the continuous flow technique. HPLC pure synthesized analog products were tested for toxicity using male mice (i.p. injection). None of them induced toxic activity.