A Comparison of the Modes of Actions of Human Salivary and Pancreatic α-Amylases on Modified Maltooligosaccharides

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Abstract
The actions of three isozymes of human pancreatic α-amylase (HPA) on phenyl α-maltopentaoside, phenyl α-maltotetraoside, and their derivatives which have an iodo, an amino, or a carboxyl group at their first or penultimate glucopyranosyl residue from the non-reducing-end were examined. The results revealed that there was no difference in the actions of the three isozymes on the modified substrates and suggested the presence of five subsites (S3 S2, S1, S1′, and S2′ and a hydrophobic amino acid residue at subsite S33 in the active site of HPA. As compared with the action of human salivary α-amylase (HSA) on the same substrates, HPA had a tendency to release more phenyl α-glucoside from every substrate; however, an iodo, an amino, and a carboxyl group of the substrates had the same effects on the binding modes of the substrates to the active site of HPA as seen in the case of the salivary enzyme. This result indicates that the three-dimensional structures of the active sites of both α-amylases are quite similar except for some minor changes at subsites S3 and S2′