Purification of xylose reductase from Candida mogii in aqueous two-phase systems

Abstract

Xylose reductase (XR) from Candida mogii was extracted by partitioning in aqueous two-phase systems (ATPS) composed of polyethylene glycol (PEG) and phosphate salts. An experimental design was used to evaluate the influence of the variables molar mass of PEG ( A), concentration of PEG ( B), concentration of phosphate ( C), and concentration of NaCl ( D) on XR extraction. The positive effect of variable B and the negative effect of A and of the interaction between A and B on the purification factor in the top phase (PF T) indicated that a simultaneous increase in PEG concentration with a decrease in molar mass of PEG leads to an increase in that response. Phosphate concentration also had a negative effect, indicating an increase in PF T with a decrease in its value. A linear model fitted to the data indicated the need to change the ranges of the variables. In a second experimental design, the influence of a lower range of PEG molar mass (MMPEG) and of tie-line length (TLL) on the partitioning of XR was studied. Quadratic models were predicted for the responses purification factor in the top phase and XR yield in the top phase ( Y T), and the maximum values predicted by these models were 1.59±0.40 and 105.8±26.2%, respectively. A 19-fold increase in the selectivity factor was experimentally achieved for a system with PEG 1000 and TLL 34. The k, PF T and Y T values corresponding to 21.21, 1.89 and 103.5 respectively were also obtained under these experimental conditions.