Influence of the immobilization process on the activity of β-galactosidase bound to Nylon membranes grafted with glycidyl methacrylate Part 1.: Isothermal behavior

beta -Galactosidase from Aspergillus oryzae has been immobilized via diazotization or condensation on Nylon membranes grafted with glycidyl methacrylate. Immobilization via diazotization occurs through tyrosine residues, while immobilization via condensation involves multipoint attachment of the enzyme to the membrane through arginine residues. It was found that the immobilization via condensation strengthens the enzyme structure in contrast to the immobilization via diazotization, giving to the membranes prepared according to the first method higher resistance to temperature and acidic solutions in comparison to those prepared with the second method. The solvent accessibility to the residues of the amino acid constituting the enzyme was studied and the 3D structure of the catalytic site was obtained by computer simulation using beta -galactosidase from Escherichia coli as template. The interpretation of the results was based on the 3D structure of the catalytic site and the arginine and tyrosine density around it. The apparent K-m values of beta -galactosidase immobilized on both membrane types are higher than those of the free enzyme, thus reducing the advantages of employing these new catalytic membranes in industrial processes. A way to overcome this drawback is indicated. (C) 2001 Elsevier Science B.V. All rights reserved.