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 chromatography demonstrated and electron microscopy confirmed the formation of tetramers and octamers. Heat inactivation studies in the range of 60° to 80°C indicated that, in contrast to a priori expectations, crosslinking via the carbohydrates decreased rather than increased thermostability. The covalently linked species, even the octamers, displayed similar activity as the native forms toward maltose and soluble starch, but activity toward raw starch was completely lost. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 63: 459–463, 1999.