Actions of starch carbohydrases on chemically modified maltodextrins

Three enzymes, potato phosphorylase, human salivary α-amylase and sweet potato β-amylase, have been studied for their actions on maltodextrins that were reduced or oxidized at C-1 of the reducing-end glucose unit. These modifications do not alter the ability of dilute solutions of the amylases to cleave the tetra-, penta-, and hexasaccharides much more rapidly than maltotriose. Modification of maltotriose, however, renders the molecule immune to the amylases. The affinities of maltotriose, -tetraose, and -pentaose as primers for potato phosphorylase in its reaction with α-glucose 1-phosphate are all diminished by chemical modification, especially by oxidation, and the modified tetraoses display the poor priming characteristics of maltotriose. It is suggested that phosphorylase and an efficient primer, such as maltotetraose, form a nondissociable complex from which the primer can only be displaced in a reaction with another such molecule.