Immobilization of L-asparaginase into a biocompatible poly(ethylene glycol)-albumin hydrogel: I: Preparation and in vitro characterization.

The feasibility of the immobilization of Escherichia coli L-asparaginase into a hydrogel matrix made of poly-(ethylene glycol) (PEG) and BSA was demonstrated. After immobilization a 200-fold increase in the Km value was observed. The use of an L-aspartic acid analogue, carbobenzoxy-L-aspartic acid and surface modification by methoxy-PEG of molecular mass 5 kDa cause a only a slight gain in affinity of the enzyme for its natural substrate. The immobilized L-asparaginase has an optimal activity over a larger range of pH than the native enzyme, owing to the effect of the matrix. At a physiological pH of 7.3, the immobilized enzyme retained 90% of its activity compared with only 43% for the native form. The immobilized enzyme retained a high proportion of its initial activity, more than 90% after 50 days of incubation at 37 degrees C, even in the presence of its substrate. This may be compared with a half-life of 2 days observed for native enzyme incubated under the same conditions. These results suggest that the BSA-PEG matrix can be very useful for enzyme immobilization and, taking into account the good biocompatibility of the matrix, one can expect that this matrix will provide a functional bioreactor for use in vivo.