Kinetic difference between hydrolyses of gamma-cyclodextrin by human salivary and pancreatic alpha-amylases

gamma-Cyclodextrin was found to be hydrolyzed by human salivary and pancreatic alpha-amylases (1,4-alpha-D-glucan glucanohydrolase, EC 3.2.1.1) at appreciable rates. The optimum pH for the enzyme reactions at 37 degrees 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 Km value (2.9 mg/ml) of pancreatic alpha-amylase for gamma-cyclodextrin was smaller than that (5.3 mg/ml) of salivary alpha-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 gamma-cyclodextrin by both enzymes took place via the multiple attack mechanism. The degrees of multiple attack by salivary and pancreatic alpha-amylases for gamma-cyclodextrin at pH 5.3 were 2.0 and 1.1, respectively. The distribution of maltodextrins produced by hydrolysis of gamma-cyclodextrin by salivary alpha-amylase was suggested to be independent of the substrate concentration, while that produced by pancreatic alpha-amylase was presumably dependent on the substrate concentration.