Extraction and stability of selected proteins in ionic liquid based aqueous two phase systems

Abstract

Ionic liquid-based aqueous two-phase extraction of a plant protein, Rubisco (Ribulose-1,5-biphosphate carboxylase oxygenase), using Iolilyte 221 PG and sodium potassium phosphate buffer, was investigated as a new alternative extraction method and compared with a conventional PEG-based two-phase system. The influence of various factors, such as the concentration of phase components, pH and temperature, on partitioning of Rubisco was evaluated by Design of Experiments. Rubisco partitions to the ionic liquid (IL) phase and the partition coefficients for the IL based two-phase system were 3–4 times higher than in a PEG-based system. Additionally, studies were done in aqueous solution of IL with varying concentrations to establish a relationship between IL concentration and protein stability. In addition to Rubisco, the stability of BSA and IgG1 was investigated in aqueous solution of two ionic liquids: Iolilyte 221PG and Cyphos 108. No fragmentation or aggregation was observed at 10% w/w concentration of the ionic liquid. However, all three proteins studied formed aggregates at 50% w/w concentration of ionic liquid. This indicates a narrow range of IL concentration for their application in protein extraction.