Comparative study on in vitro inhibition of grass carp (Ctenopharyngodon idellus) and mouse protein phosphatases by microcystins

Microcystins isolated from toxic cyanobacteria are potent inhibitors of pro tein phosphatases 1 and 2A (PP1 and PP2A). The inhibitory effects of three structural variants of microcystins (microcystin-LR, -YR, and -RR) on prote in phosphatases isolated and purified from the liver and kidney of grass ca rp (Ctenopharyngodon idellus) were investigated using the P-32 radiometric assay. The relationships between percentage inhibition of protein phosphata se activity and microcystin levels followed a typical dose-dependent sigmoi d curve. These results were compared to those obtained from mouse PP2A. The degree and pattern of inhibition of both fish and mouse protein phosphatas es by microcystins were similar. Protein phosphatases in crude fish tissue homogenates showed similar inhibition patterns as purified fish PP2A toward microcystins. (C) 2000 by John Wiley & Sons, Inc.