Binding interactions of α-amylase with starch granules: The influence of supramolecular structure and surface area

Factors affecting the α-amylase-catalysed hydrolysis kinetics of starch are incompletely understood, but are of importance to postprandial metabolism and many industrial processes (e.g. bioethanol production). Also, reports on the role of surface area and amorphous content in influencing amylolysis are conflicting. Binding kinetics of pancreatic α-amylase with native starch granules at 0 °C were compared with information on starch characteristics. Dissociation constants (Kd), obtained for amylase binding to starches of different particle sizes by solution-depletion assay, varied from 0.16 to 2.05 mg/mL. Kd was strongly dependent on specific surface area of the starch granules. Binding rates of amylase (4 nM concentration) to the starch were calculated from the time-dependency of amylase depletion and ranged from 1.95 to 22.04 × 10−3 s−1. The rates were strongly dependent on the degree of order of α-glucan chains of starch, as measured by DSC and FTIR–ATR. Thus, α-amylase binds most readily to exposed/available amorphous α-glucan chains.