Hydrolysis reactions of homopolysaccharides, which differ in their degree of branching, and mixtures of linear and branched polymers were carried out with a-amylase. The branching structures of both the original amylopectin substrate and the cluster domains of amylopectin, obtained by ethanol precipitation of the products of the action of a-amylase, were characterized via enzymatic digestion with debranching enzyme (i.e., isoamylase), followed by the fractionation of the resulting products using gel filtration chromatography. The structural properties (i.e., molecular weight, molecular weight distribution, and branching characteristics) of the resulting products during depolymerization of amylose, amylopectin, and their mixtures via a-amylase were characterized by size exclusion chromatography coupled with a low angle laser light scattering (SEULALLS) technique. It was determined that substrate branching characteristics strongly influence both the observed enzymatic activity as well as the enzyme's action pattern. A simplified kinetic model that represents the hydrolysis reactions of amylose and amylopectin mixtures via endo-acting a-amylase is proposed. We found that the reaction kinetics (i.e., enzyme affinity) was also governed by the substrate's conformation in solution. The relationships between the mass fraction of branched polymers and the kinetic parameters during a-amylolysis were compared with those predicted by the kinetic model. Excellent agreement was found between the model predictions and the experimental observations. The results reported here imply an interrelationship between enzyme action and polymeric substrate structural properties.