Imidazolium chloride-based ionic liquid-assisted improvement of lipase activity in organic solvents

The activity of a lipase from a newly isolated Pseudomonas sp. was investigated in the presence of organic solvents and imidazolium chloride-based ionic liquids (IL) such as BMIM[Cl] and HMIM[Cl]. The lipase activity in the presence of IL was higher compared to that in common organic solvents such as methanol and 2-propanol. A possible explanation for the enzyme activation might be the structural changes induced in the protein in organic systems. Since IL quench the intensity of fluorescence emission, it was not possible to investigate the major factor that influences the enzyme behavior in these new organic salts. Furthermore, the enzyme exhibited excellent activity in buffer mixtures containing both organic solvent and IL. The stability of the lipase at 50 degrees C was considerably increased in the presence of 20% BMIM[Cl] compared with the untreated lipase in aqueous medium. The light scattering method clearly showed that prevention of aggregation could be the reason for thermal stabilization at 50 degrees C in reactions containing IL. Kinetic analysis of the enzyme in the presence of different concentrations of IL showed that the K-m value increased from 0.45 mM in aqueous buffer to 2.4 mM in 50% v./v BMIM[Cl]/buffer. The increase in K-m indicates that IL can significantly reduce the binding affinity of the substrate to the enzyme. Also, a linear correlation was observed between the BMIM[Cl] concentration and V-max of the enzyme. As the concentration of BMIM[Cl] increased from 10 to 50% v./v, the V-max value increased from 1.8 to 46 mu M/min.