Role of the prophenoloxidase-activating system in invertebrate immunity

The melanization reaction, which is common response to parasite entry in invertebrate animals, especially arthropods, is due to the activity of an oxidoreductase, phenoloxidase. This enzyme is part of a complex system of proteinases, pattern recognition proteins and proteinase inhibitors constituting the so-called prophenoloxidase-activating system. It is proposed to be a non-self recognition system because conversion of prophenoloxidase to active enzyme can be brought about by minuscule and β- 1,3-glucans from micro-organisms. Several components of this system recently have been isolated and their structure determined.