Mechanism of action of human pancreatic and salivary alpha-amylase on alpha-4-nitrophenyl maltoheptaoside substrate.

We evaluated the enzymic mechanism by which alpha-4-nitrophenyl maltoheptaoside serves as a substrate for serum amylase (EC 3.2.1.1). Because polymeric substrates possess many potential sites of cleavage, the expression of enzymic activity as the number of micromoles of substrate transformed under defined conditions by an enzyme must be changed to "one microequivalent of group transformed." Therefore, we measured the activity of the isoenzymes of alpha-amylase with regard to suitable oligosaccharide substrates, which allowed us to express the catalytic activity in IUB units (U). By "high-performance" liquid chromatography we investigated the mechanism of human pancreatic and salivary alpha-amylase action, both alone and in combination with alpha-glucosidase (EC 3.2.1.20). On the basis of these results, we can describe exactly the entire reaction sequence and determine the stoichiometric coefficient of 4-nitrophenol within 0.02 mol/L (SD) produced under the assay conditions.