Different concentrations of IPTG (100 mM, 400 mM, and 1000 mM) were tested for protein induction, and protein expressions were compared using SDS-PAGE (Fig. S1). IPTG induced the
expression of both AKR and SDR at all concentrations tested,yielded target proteins with ~95% purity for AKR (Lane E2; Fig. 2a) and 98% for SDR (Lane E2; Fig. 2b). Subsequent elution fractions gave higher purities, albeit with lower protein concentrations (Lanes E3eE5; Fig. 2). Enzyme activities were measured before and after dialysis against the storage buffer (phosphate buffer), and no remarkable difference was observed, indicating that neither enzyme are affected by 0.5 M of NaCl and imidazole, contained in the elution buffer. The purification parameters of AKR and SDR are listed in Table 2. The purification method generated approximately
11-fold purification for AKR with a 38% yield, and 9-fold purification for SDR with a 31% yield.