Properties and secretory mechanism of Musca domestica digestive chymotrypsin and its relation with Drosophila melanogaster homologs

► Musca domestica larvae have 19 putatively functional chymotrypsins differentially expressed along the midgut. ► The major chymotrypsin activity was purified from the midgut and shown to prefer long substrates rather than short ones. ► The most transcribed chymotrypsin gene was cloned and expressed. ► The enzyme was immunolocalized inside vesicles (denoting exocytosis) and midgut lúmen, indicating luminal action. ► Drosophila melanogaster and M. domestica chymotrypsin genes expanded before evolutionary separation of the genera.