Kinetics of the hydrolysis of di- and trisaccharides with Aspergillus niger glucoamylases I and II

Near-homogeneous forms of glucoamylases I and II, previously purified from an industrial Aspergillus niger preparation, were used to hydrolyze a number of di- and trisaccharides linked by alpha-D-glucosidic bonds. Maximum rates and Michaelis constants were obtained at various temperatures and pH values with glucoamylase I for the disaccharides beta,alpha-trehalose, kojibiose, nigerose, maltose, and isomaltose and the trisaccharides panose and iso-maltotriose, and with glucoamylase II for maltose, maltotriose, and isomaltotriose. Maximum rates were highest and energies of activation were lowest for maltose, maltotriose, and panose, the only three substrates containing alpha-D-(1, 4)-glucosidic bonds. Michaelis constants were lowest and standard heats of binding were most negative for maltose and maltotriose. The variation of maximum rates and Michaelis constants with varying pH values suggested that two carboxyl groups were involved in substrate binding.