A Very Active α-Amylase and an Inhibitor-Based Control of Proteinases Are Key Features of Digestive Biochemistry of the Omnivorous Caribbean King Crab Maguimithrax spinosissimus

Abstract

The Caribbean king crab Maguimithrax spinosissimus is an omnivorous crustacean with high feeding plasticity. We characterized the main digestive enzymes of this crab species. Alpha-amylase and esterase activities were higher in the hepatopancreas, while those of trypsin and chymotrypsin were higher in the gastric fluid. Only one α-amylase isoform of 40 kDa generates a high α-amylase activity in this crab with a maximum at pH 5.5, 40–60°C, and 2.5 mM CaCl2. A high proteolytic activity was observed in the gastric chamber, while the activity of these enzymes was low in hepatopancreas extracts due to the presence of an inhibitor that was further demonstrated by enzyme assays and reverse zymography. Several proteases from 10 to 45 kDa are synthesized in the hepatopancreas and selectively secreted into the gut. Trypsin-like and chymotrypsin-like activities were highest at pH 7, 60°C, 0.02–1.5 M NaCl, 25 mM CaCl2. These activities were poorly influenced by Ca2+. Both enzymes were stable at a neutral to alkaline pH and a temperature up to 40°C. Esterase activity peaked at pH 9.0, 37°C, 2 M NaCl, being also poorly affected by Ca2+ but temperature sensitive. In summary, high α-amylase and protease activities, a high protease abundance, as well as a tight control over their activity by an unknown inhibitor-based mechanism appear suited for M. spinsissimus to feed opportunistically on a diet of benthic algae and epifauna with eventual carnivorous preferences.