Microcystin-LR is a potent inhibitor of type 1 and type 2A protein phosphatases (PP1 and PP2A), with IC₅₀s of 1.7 nM and 0.04 nM, respectively. IC50 & Target: IC50: 1.7 nM (PP1), 0.04 nM (PP2A)^[1]. In Vitro: Microcystins are toxic molecules produced by cyanobacterial blooms due to water eutrophication^[2]. Microcystin-LR proves to be a potent inhibitor of type 1 (IC₅₀=1.7 nM) and type 2A (IC₅₀= 0.04 nM) protein phosphatases. Microcystin-LR inhibits the activity of both type 1 and type 2A phosphatases >10-fold more potently than okadaic acid under the same conditions. Type 2A protein phosphatases in dilute mammalian cell extracts are found to be completely inhibited by 0.5 nM microcystin-LR while type 1 protein phosphatases are only slightly affected at this concentration^[1].