A STUDY OF NOVEL LECTINS AND THEIR INVOLVEMENT IN THE ACTIVATION OF THE PROPHENOLOXIDASE SYSTEM IN BLABERUS-DISCOIDALIS

Endogenous and exogenous lectins have been found to activate the proph enoloxidase (proPO) system of the cockroach, Blaberus discoidalis, to the same extent as laminarin, a previously known microbial activator o f proPO. The lectins can also further enhance this laminarin activatio n of the proPO system. Non-lectin proteins did not display any activat ion properties. The time course of proPO activation was studied after reconstitution of the reaction system using purified lectins, a trypsi n-like enzyme, a trypsin inhibitor and partially purified lectin-bindi ng proteins from the cockroach haemolymph. Lectin activation of the pr oPO system is probably not mediated by the lectin sugar-binding sites, as specific inhibitory sugars failed to abrogate the enhanced effect. The results suggest that alternative binding site(s) on the lectins m ay be involved in the proPO activation process. Evidence also suggests that several different lectins are involved in the regulation of the proPO system through separate receptor or binding molecules on the hae mocytes, and that they exert their effects early in the sequence of ev ents leading to conversion of proPO into its active form, possibly via regulation of serine proteases and protease inhibitors.