Protein phosphatases were first reported to be inhibited by microcystins by Mackintosh et. al. (1990). It was found that extremely low concentrations of microcystin-LR could strongly inhibit protein phosphatases 1 and 2A from both plants and mammals, thereby causing hyperphosphorylation of the cell and a massive disruption of a number of important cellular mechanisms.
The binding of microcystins to protein phosphatases is covalent and therefore very inhibitory and highly specific. The processes involved in the binding of microcystins to protein phosphatases is the subject of some research.