The unicellular marine dinoflagellate, Prorocentrum lima, an established producer of okadaic acid (OA), was shown to contain a type-1 protein phosphatase (PP-1) the biochemical profile of which on Mono-Q and Superdex-75 fast protein liquid chromatography was identical to the catalytic subunit of PP-1 from rabbit skeletal muscle. Purified P. lima PP-1 (apparent molecular mass 37.5 kDa) was highly sensitive to inhibition by mammalian protein phosphatase inhibitor-1 and inhibitor-2, and to OA itself. A 6–7-fold increase in OA production by P. lima, when grown under controlled conditions, correlated with an up to 300-fold increase in P. lima PP-1 activity. Furthermore, P. lima did not contain any detectable type-2A protein phosphatase activity. This study represents the first identification of a serine/threonine protein phosphatase in a dinoflagellate.
