PROPHENOLOXIDASE ACTIVATING SYSTEM IN TUNICATE HEMOLYMPH

The activation sequence and related factors of the prophenoloxidase ac tivating system in crustaceans was compared with the equivalent system in tunicates. Both solitary and colonial ascidians present in their h emolymph a copper-dependent phenoloxidase activity that may be inhibit ed by tropolone and phenylthiourea. Carbohydrates are able, to various extents, to trigger proPO system which requires serine protease cleav age for activation to phenoloxidase (PO). In some ascidians, hemocytes called <<morula cells>> show PO activity, while in Ciona intestinalis the <<univacuolar refractile granulocytes>> are positive after cytoch emical staining with L-dopa. The relationships between proPO system an d defence reactions (opsonic, cytotoxic) of ascidians are discussed.