Description_x000D_ General description_x000D_ Microcystin is a small, monocyclic peptide, composed of seven amino acids connected via peptide bonds. It is a cyanotoxin with hepatotoxic and tumor promoting properties. Several algal genera like Anabaena, Aphanizomenon, Microcystis and Planktothrix produce microcystin. Microcystin has four congeners namely, -LR, -LA, -YR and -RR._x000D_ Application_x000D_ Microcystin LA from algae has been used as a standard for liquid chromatography/mass spectrometry (LCMS) for toxin analysis._x000D_ Biochem/physiol Actions_x000D_ Microcystin LA inhibits protein phosphatase type 2A and protein phosphatase type 3 more potently than protein phosphatase type 1 (order of potency PP2A > PP3 > PP1). Induces neutrophil-activating chemokines and extracellular reactive oxygen species, possible mechanisms of its hepatotoxic effects.