Biosynthesis of Astacus protease, a digestive enzyme from crayfish.

For the first time, the site of biosynthesis of a well characterized invertebrate digestive enzyme is localized. The enzyme chosen, Astacus protease, is a zinc-metalloenzyme occuring in high concentration in the gastric fluid of the freshwater crayfish Astacus astacus. Enzyme production was stimulated in adult crayfish either by feeding or by removal of the gastric fluid. Immunohistochemistry, cytology and investigation with radioactive tracers demonstrate that in the hours following stimulation, new enzyme was produced in the F-cells of the midgut gland and subsequently discharged into the midgut gland lumen. The enzyme was then accumulated and stored extracellularly in the cardiac stomach in active form. The mechanism of enzyme production observed in Astacus differs considerably from vertebrates suggesting an alternative model for synthesis and storage of digestive enzymes.