The mechanism of carbohydrase action. 5. Action of human salivary α-amylase on amylopectin and glycogen

Abstract

Amylopectin (waxy-maize starch) is degraded by low concentrations of human salivary [alpha]-amylase to yield maltose (42%), maltotriose (28%) and [alpha]-limit dextrins containing the [alpha]-1,6-branch links of the amylopectin. Glycogen gives the same products. The smallest [alpha]-limit dextrin is a pentasaccharide, the [alpha]-l,6-link of which is split by R-enzyme to yield maltose and maltotriose. [alpha]-Limit dextrins containing 2 and 3 branch links per molecule are also present. The maltodextrins formed by R-enzyme action on the mixed [alpha]-limit dextrins have been separated, identified and analyzed. An hypothesis to explain the formation of the limit dextrins has been formulated. It is suggested that under the chosen experimental conditions three [alpha]-1,4-bonds in defined positions adjacent to the branch link are resistant to o-amylase action. The hypothesis accounts for the presence of the [alpha]-limit dextrins containing more than one branch link only if the parent polysaccharides exhibit multiple branching. By quantitatively analyzing the products of [alpha]-amylolysis and those formed on subsequently debranching the [alpha]-limit dextrins, the proportions of [alpha]-l,6-links in amylopectin and glycogen have been calculated. The results agree with the measured proportions of non-reducing-end groups and it is concluded that salivary [alpha]-amylase does not split the [alpha]-l,6-links in these polysaccharides.