INHIBITION OF AN ARCHAEAL PROTEIN PHOSPHATASE-ACTIVITY BY OKADAIC ACID, MICROCYSTIN-LR, OR CALYCULIN-A

Soluble extracts of the methanogenic archaeon, Methanosarcina thermoph ila TM-1, contained a divalent metal ion-stimulated protein-serine pho sphatase activity. This activity was sensitive to micromolar concentra tions of okadaic acid, microcystin-LR, or calyculin A. three compounds thought to be highly specific inhibitors of the type 1/2A/2B genetic superfamily of eukaryotic protein-serine/threonine phosphatases. The o bservation that each of these three chemically unrelated compounds inh ibited this archaeal protein phosphatase activity suggests the existen ce of structural homology, and perhaps even common genetic ancestry, w ith the type 1/2A/2B superfamily of protein-serine/threonine phosphata ses found in eukaryotic organisms.