Solubilisation of α-chymotrypsin by hydrophobic ion pairing in fluorous systems and supercritical carbon dioxide and demonstration of efficient enzyme recycling

Abstract

Hydrophobic ion-pairing (HIP) with the fluorinated surfactant KDP 4606 (KDP) was used to extract the protein α-chymotrypsin (CMT) into perfluoromethylcyclohexane (PFMC). The diameter of the solubilised CMT-KDP complexes formed in PFMC was determined by dynamic light scattering (DLS) to be 25 nm which suggested the formation of a protein aggregate containing ∼100 protein molecules surrounded by KDP 4606 surfactant molecules per particle. The catalytic activity of the protease CMT either solubilised by HIP or as the suspended native enzyme has been investigated in both a fluorous biphasic system (FBS) and a supercritical carbon dioxide (scCO2) batch reactor. Transesterification of N-acetyl-L-phenylalanine ethyl ester (APEE) with n-butanol or rac-2-butanol was catalysed by the protease in the FBS hexane-PFMC or scCO2 at 40 °C. Under comparable conditions, the amount of transesterification of the solubilised protease–surfactant (CMT-KDP) complex in PFMC (6–10%) was shown to be significantly higher than that of the suspended protease (1–3%) in either hexane–PFMC or scCO2. This suggested the formation of a catalytically active CMT-KDP aggregate in PFMC. The CMT-KDP complex which is retained in the fluorous phase on cooling the solution was successfully reused over four cycles with no loss of activity.