The prophenoloxidase activating system of the shrimp Penaeus paulensis and associated factors

In the present study we investigated the proPO activating system of the penaeid Penaeus paulensis, focusing on its role in the shrimp immune system. The great majority of PO activity (more than 90%) was found in the shrimp hemocytes. The enzyme activity was greatly enhanced by components of microorganism cell walls, such as LPS and beta-1,3-glucans, suggesting its involvement in non-self recognition. PO activity was also found in the shrimp serum and trypsin, and LPS were able to increase the enzyme activity. Thus, serum can be used as an alternative for the study of the shrimp proPO activating system, as it is much more readily obtained than HLS. PO activity was cation-dependent, and 5 mM of calcium and 10 mM of magnesium were the optimal concentrations for the enzyme activity. An immune factor was found in the shrimp HLS, capable of inducing cell-adhesion and degranulation of the penaeid hemocytes.