Subsite profile of the active center of porcine pancreatic alpha-amylase. Kinetic studies using maltooligosaccharides as substrates.

The hydrolysis of several maltooligosaccharides catalysed by porcine pancreatic alpha-amylase was performed in order to determine their kinetic parameters. Maltose behaves as a substrate. Molecular activity (Ko) increases with chain length up to maltopentaose, remaining practically unchanged from maltopentaose to maltoheptaose. Maltose shows the highest Km value while the one for maltotriose is the lowest. Only maltose and maltotriose were directly cleaved to glucose. From Km and Ko values, the binding energy of the total complexes and of the productive ones respectively were calculated. The binding energy at each subsite was determined assuming that each substrate forms a single productive complex and that maltose and maltotriose differ in their binding mode from higher oligosaccharides. The model was checked by calculating theorical Km and Ko. Theorical values agree reasonably well with experimental ones.