Microcystin-LR

Inhibitor of PP1 and PP2A

Heptapeptide ester hepatotoxin. Tumor promoter. Equally potent and selective inhibitor of protein phosphatase 1 (PP1) and 2A (PP2A). PP2B is less sensitive and PP2C is not inhibited up to 4 µM. Useful for affinity-purification of PP2A. The product is not cell permeable except in liver cells, which appear to have a functional uptake system. Is absorbed by hepatocytes via the multispecific organic anion transporter. Does not induce any effects on mouse skin or human fibroblasts due to cell membranes impermeability. Has no effect on protein kinases. Less toxic than the more hydrophobic analogs microcystin-LY, -LW and -LF. Frequently contaminates fresh-water lakes and ponds. Causes livestock poisonings. Ozonation did lead to complete loss of toxicity and toxins from contaminated samples.

Isolated from Microcystis aeruginosa.