IDENTIFICATION OF A CYCLIC AMP‐DEPENDENT PROTEIN KINASE IN THE DINOFLAGELLATE AMPHIDINIUM OPERCULATUM

Abstract

Cyclic AMP is an important signaling molecule in both prokaryotes and eukaryotes. In eukaryotes, the action of cyclic AMP is mediated by cyclic AMP‐dependent protein kinase (PKA). Efforts to identify PKA in dinoflagellates have met with mixed success in previous studies. In Amphidinium operculatum, we have identified the presence of cAMP, and observed cell cycle inhibition by the cAMP pathway inhibitor, isobutyl methylxanthine, suggesting the presence of a eukaryotic cAMP pathway. However, crude lysates of A. operculatum failed to show in vitro kinase activity toward kemptide, a specific substrate of mammalian PKA. This may reflect the presence of unidentified low molecular weight inhibitors, because when cell lysates were fractionated by gel filtration chromatography, cAMP dependent kinase activity was identified. The molecular weight of this PKA was 66 kDa, much smaller than bovine PKA (250 kDa), but similar to that reported in the diatom Cylindrotheca (78 kDa). Current work is focusing on characterization of subunit structure of the PKA of A. operculatum, as compared with bovine PKA.