Crosslinking of glucoamylases via carbohydrates hardly affects catalysis but impairs stability

Mild oxidation of glucoamylases from Aspergillus niger (E.C.3.2.1.3.) with periodate, followed by incubation with adipic acid dihydrazide, covalently linked enzyme molecules via their glycosyl groups. Size exclusion chromatog raphy demonstrated and electron microscopy confirmed the formation of tetra mers and octamers. Heat inactivation studies in the range of 60 degrees to 80 degrees C indicated that, in contrast to a priori expectations, crosslin king via the carbohydrates decreased rather than increased thermostability. The covalently linked species, even the octamers, displayed similar activi ty as the native forms toward maltose and soluble starch, but activity towa rd raw starch was completely lost. (C) 1999 John Wiley & Sons, Inc.