The observed higher stability of D114C CLECs in the presence of organic co-solvents enabled also the use of significantly higher substrate concentrations in the azidolysis of 1. Specifically, D114C CLECs were still active at the highest substrate concentration tested (200 mM 1 at 20% (v/v) isopropanol), while soluble enzyme was fully inactive already (Figure ). This result further confirms the significantly increased stability of D114C CLECs in the presence of water-miscible organic solvents.