Kinetic difference between hydrolyses of γ-cyclodextrin by human salivary and pancreatic α-amylases

Abstract

γ-Cyclodextrin was found to be hydrolyzed by human salivary and pancreatic α-amylases (1,4-α-d-glucan glucanohydrolase, EC 3.2.1.1) at appreciable rates. The optimum pH for the enzyme reactions at 37°C in the presence of 0.1 M NaCl was at around pH 5, which was remarkably different from the optimum pH (pH 6.9) of the enzymes for starch. The K_m value (2.9 mg/ml) of pancreatic α-amylase for γ-cyclodextrin was smaller than that (5.3 mg/ml) of salivary α-amylase at pH 5.3, while the V value of the former was 3.7-times larger than that of the latter. The hydrolyses of γ-cyclodextrin by both enzymes took place via the multiple attack mechanism. The degrees of multiple attack by salivary and pancreatic α-amylases for γ-cyclodextrin at pH 5.3 were 2.0 and 1.1, respectively. The distribution of maltodextrins produced by hydrolysis of γ-cyclodextrin by salivary α-amylase was suggested to be independent of the substrate concentration, while that produced by pancreatic α-amylase was presumably dependent on the substrate concentration.