Production and purification of tartrate dehydrogenase. Role of aqueous two-phase extraction

Tartrate dehydrogenase (TDH) is a stereospecific intracellular enzyme produced by Pseudomonas putida. Several methods for separation of nucleic acids from the proteins in cell homogenate were compared in this study. These methods included precipitation (using streptomycin sulfate, manganous sulfate, and protamine sulfate) and aqueous two-phase extraction. Under optimal conditions of separation, a single-step aqueous two-phase extraction followed by back-extraction of the enzyme from enzyme-rich PEG-phase resulted in 77% recovery of enzyme. This compared favorably with 50% enzyme recovery using protamine sulfate treatment. Furthermore, the remaining enzyme activity was accounted in the nucleic acid-rich dextran phase and the spent-PEG phase, suggesting that a multistep extraction process would increase enzyme recovery even more. Under the conditions of aqueous two-phase extraction, the selectivity of proteins over nucleic acids was 30, indicating a high degree of separation of proteins and nucleic acids in this process. The experimental data and their implications are presented.