unambiguously show that the membrane discs were recyclable. In all cases, the same final conversion (close to thermodynamic equilibrium) could be reached. More importantly, specific activity (approached by initial activity) was not affected throughout the successive catalytic cycles. This result paves the way toward a possible use of membrane-immobilized enzymes in continuous flow processes. Such robustness and recyclability was also confirmed with the Sselective HeWT enzyme (Figure ), as no significant decrease of specific activity could be observed throughout the cycles. Another interesting aspect to investigate was the ability of the biocatalytic membrane to work in the absence of externally added co-factor (PLP). Such ability has already been reported on PEI-coated supports, onto which both PLP and TA could be co-immobilized . This aspect would be particularly important in the perspective of a continuous flow membrane reactor, since it would allow to get rid of the costly PLP feed during the operation. Hence, TsRTA_PP3 (for which only the TA immobilization step is done in the presence of PLP) was tested in successive catalytic cycles without adding PLP to the reaction media (Figure ). In such case, the residual activity dropped after each reaction cycle (i.e. down from 78 % to 23 % after five cycles). This suggests a significant PLP leaching leading to immobilized TA deactivation. In order to overcome this problem, we slightly adapted the immobilization process. Inspired from López-Gallego et al. we implemented a two-step immobilization.