The functionalized PP membrane was transferred into 5 mL of buffered solution (HEPES 0.1 M buffer, PLP 1 mM, sodium pyruvate 10 mM) containing the desired TA concentration (C0) at pH 8, and incubated for 18 hours at 35 °C under gentle stirring (Figure , step 3). After immobilization, the resulting membrane-immobilized transaminase was rinsed with 5 mL of rinsing solution (containing PLP 1 mM, sodium pyruvate 10 mM in HEPES 0.1 M buffer pH 8) for 30 minutes (repeated two times) to eliminate the loosely attached TAs. For comparison, this TA immobilization was also performed on each PP membrane support employed in this study (i.e. PP, PP_PDA, PP_PDA_GDE and PP_PDA_GDE_PEI). The resulting catalysts were denoted TA_PPy, where y = / stand for TAs immobilized on pristine PP, y = 1 on PP_PDA, y = 2 on PP_PDA_GDE and y = 3 on PP_PDA_GDE_PEI.