In vitro neutralization of the inhibitory effect of Microcystin-LR to protein phosphatase 2A by antibody against the toxin.

Microcystin-LR (MCYST-LR) was found to be a very potent protein-phosphatase 2A (PP2A) inhibitor at an ID50 as low as 0.1 nM. Comparing to calyculin A and okadaic acid, MCYST-LR was found to be about 100 times stronger than calyculin A and okadaic acid for their inhibition to PP2A. The inhibitory effect on PP2A by MCYST-LR was abolished when antibodies against MCYST-LR were present in the assay system. Polyclonal antibodies were more effective than monoclonal antibodies in reversing the inhibitory effect. A dose-dependent neutralization of the inhibitory effect of MCYST to PP2A by anti-MCYST polyclonal antibodies were observed. Almost 80% of the enzyme activity was restored when as low as 0.012 micrograms of Pab was present. The specific reaction caused by the antibody was evident from an analysis that the antibodies had no effect on reversing the inhibition of PP2A caused by okadaic acid and calyculin A.