Recombinant Bacillus sphaericus phenylalanine dehydrogenase (PheDH) partitioning was studied in polyethylene glycol (PEG) and ammonium sulfate aqueous two-phase systems (ATPS). The objectives of this work were to investigate influences; varying the molecular mass and concentration of PEG, pH, phase volume ratio (V(R)), tie-line length (TLL) and concentration of (NH(4))(2)SO(4) on the partition behavior of PheDH. It was revealed that the partitioning was not affected by VR, while PEG molecular mass and concentration and (NH4)2SO4 concentration had significant effects on enzyme partitioning. Longer TLL and higher pH resulted in better partitioning into the top phase. Under the most favorable partition conditions with 8.5% (w/w) PEG-6000, 17.5% (w/w) (NH4)2SO4 and V(R) = 0.25 at pH 8.0, partition coefficient (K(E)), recovery (R%), yield (Y%) and TLL were achieved 58.7%, 135%, 94.42% and 39.89% (w/w), respectively. Overall, the promising results obtained in this research indicated that the ATPS partitioning can be provided an efficient and powerful tool for recovery and purification of recombinant PheDH. (c) 2007 Elsevier Ltd. All rights reserved.