Effect of increasing co-solvent concentration on the stability of soluble and immobilized β-galactosidase

The effect of increasing concentration of co-solvents on the stability of both soluble and immobilized E. coli p-galactosidase was studied. The enzyme was immobilized on to glutaraldehyde-agarose and the co-solvents tested were: NN-dimethylformamide (DMF), ethanol, acetone, and dioxane (6-36% v/v). Deactivation kinetics were analyzed according to the,two-step deactivation model proposed by Henley and Sadana. A multi-temperature study revealed that the immobilized derivative is considerably more stable than the soluble enzyme, even at high temperature where the half life of the soluble enzyme is less than I h. Enzyme immobilization did achieve thermal and solvent stabilization at low concentrations, but this task proved more difficult with increasing co-solvent concentrations. In the case of ethanol and acetone, with the increase in co-solvent concentration, the immobilized derivative became less stable than the soluble enzyme. Immobilization may impose certain constraints on the protein structure which have the effect of sensitizing it to denaturation at high co-solvent concentrations. Complementary stabilization strategies are, therefore, being studied. (C) 2002 Elsevier Science B.V. All rights reserved.