A comparison of phenoloxidase activity in the blood of marine invertebrates.

A range of marine invertebrates were screened for prophenoloxidase (a marker protein of the prophenoloxidase activating system) in the coelomic fluid or hemolymph. The crustaceans and the ascidian, Ciona intestinalis, displayed strongest activity, with low levels found in the starfish, Asterias rubens, the sea urchin, D. antillarum, and the brachiopod, Liothyrella uva. The enzyme appeared to be absent from the isopod, Glyptonotus antarcticus. Further analyses of the blood cells of selected species revealed that prophenoloxidase tends to reside in the granular-type cells or their equivalent, and in the crustaceans and C. intestinalis is activated by lipopolysaccharides. In arthropods, prophenoloxidase is known to represent the terminal component of a complex cascade of enzymes that functions in non-self-recognition and host defence. The present study establishes that the enzyme is present in the blood cells of most, but not all, crustaceans and occurs in certain other invertebrate species, notably the urochordate, C. intestinalis.