Prophenoloxidase has been successfully obtained from the haemolymph of the cockroach Peviplaneta americana using cane sugar saline solution, The proenzyme was activated by various exogenously added proteases such as chymotrypsin, trypsin, subtilisin and thermolysin. Thermolysin was found to be the greatest activator, followed by chymotrypsin and subtilisin. Chymotrypsin activation showed a lag period when compared with the other proteases tested, indicating that activation by chymotrypsin followed an indirect path, whereas, subtilisin and thermolysin activated the proenzyme directly. Exogenously added protease inhibitor showed inhibition towards protease-mediated prophenoloxidase activation, Benzamidine inhibited chymotrypsin and trypsin activation, whereas soybean trypsin inhibitor inhibited trypsin, In situ inhibitor isolated from the haemocytes of Periplaneta americana inhibited the prophenoloxidase activation and showed evidence for the presence of a built-in inhibition system for the release of the components of the prophenoloxidase activating system of P. americana, Electrophoretic localization of activated phenoloxidase showed two bands, suggesting the dimeric condition of high mel. wt prophenoloxidase.
