FUNCTIONAL-ANALYSIS OF PLASMA PROPHENOLOXIDASE SYSTEM IN THE MARINE MUSSEL PERNA-VIRIDIS

The role of prophenoloxidase (proPO) system in recognition and phagocy tosis of yeast cells by hemocytes was examined in vitro using whole pl asma and proPO system isolated from the plasma of the marine mussel, P erna viridis. The proPO was isolated from the plasma by ammonium sulph ate precipitation and gel filtration. The final proPO preparation was homogeneous in native PAGE, and could be activated by trypsin, alpha-c hymotrypsin and pronase-E. Laminarin (a polymer of beta-1, 3-glucan) a nd lipopolysaccharides (LPS) from diverse bacterial species effectivel y activated the isolated proPO, demonstrating the ability of this proe nzyme to interact directly with microbial surface components. The susc eptibility of proPO activation to inhibition by serine protease inhibi tors such as soybean trypsin inhibitor (STI) or p-nitrophenyl-p'-guani dinobenzoate (p-NPGB), indicates that the isolated fraction may contai n an integral serine protease domain in an inactive state. The presenc e of laminarin- or LPS-activated whole plasma of P. viridis facilitate d adherence of yeast cells to hemocyte surface as well as eventually s timulated phagocytic uptake of the target cells by hemocytes, and no s uch hemocytic response was recorded with STI controls. This and other results strongly suggest that the intermediary factors generated durin g activation of plasma proPO system by non-self molecules play a key r ole in recognition and opsono-phagocytosis by hemocytes. However, the proPO system isolated from P. viridis plasma, after activation with mi crobial surface components, failed to show an opsonic effect. (C) 1998 Published by Elsevier Science Inc. All rights reserved.