IN-VITRO NEUTRALIZATION OF THE INHIBITORY EFFECT OF MICROCYSTIN-LR TOPROTEIN PHOSPHATASE 2A BY ANTIBODY AGAINST THE TOXIN

Microcystin-LR (MCYST-LR) was found to be a very potent protein-phosph atase 2A (PP2A) inhibitor at an ID50 as low as 0.1 nM. Comparing to ca lyculin A and okadaic acid, MCYST-LR was found to be about 100 times s tronger than calyculin A and okadaic acid for their inhibition to PP2A . The inhibitory effect on PP2A by MCYST-LR was abolished when antibod ies against MCYST-LR were present in the assay system. Polyclonal anti bodies 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 obser ved. Almost 80% of the enzyme activity was restored when as low as 0.0 12 mu g of Pab was present. The specific reaction caused by the antibo dy was evident from an analysis that the antibodies had no effect on r eversing the inhibition of PP2A caused by okadaic acid and calyculin A .