Enkephalin-degrading Activity in Arthropode Hemolymphe

Enkephalin and related peptides are rapidly inactivated in Astacus fluviatilis and Limulus polyphemus hemolymphe. At least three different enzymes, an amino-peptidase, a carboxypeptidase and a peptidyl-dipeptidase, acting concomitantly on the peptide substrates have been identified. The properties of these enzymes were characterized and they were compared to similar enzymes of the vertebrate blood. The opioid peptides appear to be extremely short lived in invertebrate hemolymphe, which presumably is a metabolic barrier to the action of active peptides stronger than vertebrate blood.