Activation of prophenoloxidase in the plasma and haemocytes of the marine mussel Perna viridis Linnaeus.

Phenoloxidase activity was detected in plasma and haemocytes of the marine mussel Perna viridis. This enzyme exists as a proenzyme, prophenoloxidase (proPO), in both these haemolymph fractions and could be activated in vitro by exogenous proteases (trypsin and alpha-chymotrypsin) and a detergent (sodium dodecyl sulphate). In addition, laminarin (a polymer of beta-1,3 glucan) and bacterial lipopolysaccharides (LPSa) effectively triggered proPO activation in these haemolymph fractions. The activation of proPO by non-self molecules was dependent upon calcium ions at a low concentration. This activation process appeared to involve a limited proteolysis, since serine protease inhibitors (soybean trypsin inhibitor, benzamidine or p-nitrophenyl-p'-guanidinobenzoate) suppressed conversion of proPO to the active enzyme. This study demonstrates the selective response of plasma and haemocytic proPO to activation by different types of bacterial LPS tested and suggests that proPO system in both plasma and haemocytes of P. viridis serves an important function in non-self recognition and host immune reactions.