Inspired López-Gallego et al. , we immobilized the enzyme onto PP_PDA_GDE_PEI (with either 0.1 mM or 1 mM PLP, sodium pyruvate 10 mM in HEPES 0.1 M buffer pH 8) and then rinsed the resulting membrane three time (5 mL sodium pyruvate 10 mM in HEPES 0.1 M buffer pH 8), and directly incubated it with PLP (1 mM in HEPES 10 mM pH 8 for 90 minutes at room temperature under gentle stirring). Additional rinsing was applied again (four times 5 mL sodium pyruvate 10 mM in HEPES 0.1 M buffer pH 8, 30 minutes). The obtained membranes were denoted TA_PP3_SSz, where z is the concentration of PLP (in mM) used during the TA immobilization step. The amount of PLP effectively loaded onto the membrane was evaluated by UV absorption (see ESI).