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

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 (PFT) 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 PFT 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, PFT and Y-T values corresponding to 21.21, 1.89 and 103.5 respectively were also obtained under these experimental conditions. (C) 2003 Elsevier B.V. All rights reserved.