2.2. Cultivation of E. coli Cells as a Substrate for Lys394

A total of 20 mL of E. coli culture was added to 250 mL of LB-Lennox solution and held for 20 h at 37 °C. Cells were deposited using a Jouan BR4i (France) centrifuge for 15 min at 1500× g and re-suspended in 40 mL of 10 mM Tris/HCl buffer at pH 8.2. After repeating the above deposition–resuspension procedure, the cell culture was diluted using the same buffer to reach an optical density of OD600 = 1.0. The resulting suspension was divided into 200 µL aliquots and stored at −70 °C for a month. The suspension was then defrosted just before the measurements.