Studies of the effect of maltose on the direct binding of porcine pancreatic α-amylase to maize starch

For a two phase system comprising an enzyme in solution acting on an insoluble substrate such as starch, adsorption of the enzyme is a key initial step in the reaction but few studies of agents affecting direct binding have been performed. The effect of maltose on the interaction of maize starch with porcine pancreatic α-amylase was studied by using a method in which the direct binding of starch to amylase is measured under conditions of negligible catalytic activity. The dissociation constant for starch binding increased with maltose concentration and analysis of the binding showed that the kinetic action of maltose was entirely competitive. This result accords with results described in the literature in which maltose was shown to be a competitive inhibitor of amylase action. If the maltose concentration is sufficiently high, a second molecule may bind at the active site but the affinity of the second binding step is approximately 6.5-fold weaker. Because of the relatively low affinity for maltose, it seems unlikely that inhibition by maltose of the initial stage of starch-amylase interaction normally plays any role in regulating intestinal digestion of starch.