Abstract
Extracts of fifty-seven newly isolated strains of dinoflagellates and raphidophytes were screened for protein phosphatase (PP2A) inhibition. Five strains, identified by rDNA sequence analysis as Prorocentrum rhathymum, tested positive and the presence of okadaic acid was confirmed in one strain by HPLC-MS/MS and by HPLC with fluorescence detection and HPLC-MS of the okadaic acid ADAM derivative. Quantitation of the ADAM derivative indicated that the concentration of okadaic acid in the culture medium is 0.153 microg/L.