Isocitrate dehydrogenase from Escherichia coli displays high solvent tolerance during NADPH generation

Isocitrate dehydrogenase (ICDH) is the key enzyme of the Krebs cycle where it catalyzes the NAD(P)⁺-dependent oxidative decarboxylation of isocitrate to α-ketoglutarate. Despite the identification and characterization of several ICDHs from different organisms, the solvent and salt tolerance abilities of these enzymes have not been explored. In the current work, the NADPH-dependent isocitrate dehydrogenase from E. coli (EcICDH) has been investigated for its activity at varying solvent and salt concentrations. EcICDH retained high activity in the presence of up to 50% EtOH and iso-propanol and tolerated high KCl concentrations up to 150 mM. Furthermore, the isocitrate/EcICDH system was evaluated for NADPH generation during the reduction of 2-tetralone, a seven-membered cyclic imine, and 2-nitro chalcone substrates with naphthol, imine, and ene reductases, respectively, to show its utility.