Molecular mechanism in alpha-glucosidase and glucoamylase

The hydrolysis of glucosidic linkage catalyzed by every carbohydrate-hydrolase is a reaction in which the product retains (alpha-->alpha or beta-->beta) or inverts (alpha-->beta or beta-->alpha) the anomeric configuration of the substrate. alpha-Glucosidase and glucoamylase are essentially distinguished by releasing alpha-glucose and beta-glucose, respectively, from the common substrates having alpha-glucosidic linkage. The distinction in the substrate specificities of the two enzymes was explained by the subsite affinities in their active sites. The amino acid sequences of the regions containing the catalytic sites were compared in alpha-glucosidases and glucoamylases from various sources. alpha-Glucosidases were suggested to be grouped into two families by their primary structures. The catalytic reaction mechanisms of carbohydrate-hydrolases were discussed in the two significant models of a nucleophilic displacement mechanism and an oxocarbenium ion intermediate mechanism.