TAs were immobilized on the membranes described above and tested in the kinetic resolution of BMBA. Figure shows the activity (in terms of BAP yield) displayed by the different heterogeneous biocatalysts obtained by the immobilization of TsRTA on the different membrane supports. When using the pristine PP or PAN membranes as supports for the enzyme, the activity was virtually nil. However, upon functionalizationand depending on the parameters of functionalization and immobilization (vide infra)significant biocatalytic activity was observed. In general, PP-immobilized TAs exhibited superior performance as compared to the PAN-immobilized TAs. Similar activity trends were obtained when employing HeWT as immobilized transaminase on these supports (Figure ). To interpret the raw yields obtained with the different enzyme-loaded membranes, complementary indicators must be considered. Table gathers the immobilization yield, specific activity recovery, and leaching fraction displayed by the obtained membraneimmobilized TAs, for both immobilization strategies. Regarding the HPAN_PEI immobilized biocatalysts, it can be observed that the immobilization yield is boosted when the TA immobilization was performed at pH 5.5 (HeWT_HPAN1b and TsRTA_HPAN1b) rather than 8 (HeWT_HPAN1a and TsRTA_HPAN1a). This can be explained by the fact the PEI is more positively charged at low pH and favors the electrostatic adsorption of a larger amount of TA at the membrane surface. Accordingly, the observed activity is higher. Importantly, the specific activity (activity normalized by the amount of immobilized TA on the membrane) was the same, which indicates that, on average, the intrinsic activity of each additional immobilized transaminases was maintained. However, leaching after catalytic test was important, highlighting the need of post-treatment strategies to improve the anchoring of the immobilized TAs at the membrane surface.