Modulation of immobilized enzyme activity by altering the hydrophobicity of nylon-grafted membranes - Part 2: Non-isothermal conditions

Lactose hydrolysis by beta-galactosidase immobilized on two nylon membranes, differently grafted, has been studied in a bioreactor operating under isothermal and non-isothermal conditions. One membrane (M-1) was obtained by chemical grafting of methylmethacrylate (MAA); the other one (M-2) by a double chemical grafting: styrene (Sty) and MAA. Hexamethylenediamine was used as a spacer between the grafted membranes and the enzyme. Both membranes have been physically characterized studying their permeabilities in presence of pressure or temperature gradients. Under non-isothermal conditions, the increase in activity of membrane M-2 was higher than that of membrane M-1. The alpha and beta coefficients, giving the percentage of activity increase when a temperature difference of 1 degrees C is applied across the catalytic membranes, have been calculated. Results have been discussed with reference to the greater hydrophobicity of membrane M-2 with respect to membrane M-1, the hydrophobicity being a prerequisite for the occurrence of the process of thermodialysis. (C) 2000 Elsevier Science B.V. All rights reserved.