Similar beneficial effect of such GA cross-linking of PEI-immobilized enzymes have been previously documented, with positive effects on specific activity (with lipases ), or on stability and reusability (with TAs 70 ). In fact, here, TA enzymes are not only cross-linked together but also bound to PEI via GA. We surmise that bonding occurs preferentially with PEI (rather than cross-linking). Hence, one hypothesis is that the higher specific activity obtained for TAs_HPAN3b is linked to a more favorable (more hydrated, less constrained) chemical microenvironment conferred by the PEI layer to the immobilized TAs .