Temperature and pH characteristics of amylase and proteinase of adult freshwater pearl mussel, Hyriopsis (Hyriopsis) bialatus Simpson 1900

Abstract

The enzymatic properties of the main digestive enzymes, amylase and proteinase, from stomach and intestine of adult freshwater pearl mussel, Hyriopsis (Hyriopsis) bialatus Simpson 1900, were studied at various pH's (1–11) and temperatures (20–80 °C) as well as their enzymatic stability at various pH's. The pH and temperature profiles of the enzymatic activities of amylase and proteinase were similar between male and female mussels. At least seven amylase activities were observed in both stomach and intestine. Four acidic amylases showing pH stability at 2–11 had temperature optima at 35, 45, 55 and 65 °C. Two neutral amylases with pH stability at 6–7 showed temperature optima at 30 and 40 °C, and alkaline amylase(s) with pH stability at 8–10 had temperature optima range at 60–75 °C. Proteinase, on the other hand, showed its optimal activity at pH 5 (acidic proteinase) and at 60–70 °C in the stomach, while at a pH range of 6–8 (alkaline proteinase) and at 35–40 °C in the intestine. A wide pH stability range was observed for both acidic proteinase (pH 2–6) and alkaline proteinase (pH 4–7). Six proteinase activities were differentiated, two acidic forms with pH stability at 2–3 and 6 having respective optimal temperature at 60 and 70 °C, and four alkaline forms with pH stability at 4, 6, 7 and 10 showing respective optimal temperature of 25, 40, 35 and 55–80 °C. Digestive enzymes seemed to be more sensitive in females than in males. Females seemed to prefer a more alkaline condition for optimal food digestion compared to male mussels, as their alkaline proteinases were less stable in acidic conditions. At optimal conditions, both amylase and proteinase enzymes showed higher specific activities in the stomach than in the intestine. At habitat temperature (28–30 °C), amylase specific activities dominate in the stomach, while both amylase and proteinase specific activities dominate in the intestine.