Soluble and membrane-bound Met-enkephalin degrading peptidases in Mytilus edulis hemolymph

Recent reports have provided strong evidence indicating that Met-enkephalin is serving as a neuroimmune modulator. It acts as a bidirectional signal molecule in transmitting message between the endocrine system and the immune cells in the circulating fluid. In this study, we investigated peptidases which are capable of degrading Met-enkephalin in the hemolymph fluid and hemocyte membrane. Our results showed that aminopeptidase is present at a high level in the fluid and a low level in the membrane. Carboxypeptidase is not present in the fluid but it is present at a level higher than that of aminopeptidase in the membrane. Either ACE or neutral endopeptidase is also present in the hemolymph fluid and hemocyte membrane. Functional role of these peptidases in the overall scheme of the neuroimmune mechanism is currently under investigation.