Evaluation of crude dextran as phase-forming polymer for the extraction of enzymes in aqueous two-phase systems in large scale

A detailed study of the influence of crude dextran on enzyme extractions in aqueous phase systems is presented in this article. The physical parameters of crude dextran, a purified T‐500 fraction from Pharmacia, and a hydrolyzed crude dextran are compared and their influence on the phase system parameters investigated. Initially there is a drastic increase in the viscosity of the lower dextran‐rich phase and a significant shift in the macroscopic structure of these phases, observed as the “gel‐forming” properties of the dextran phases. The latter can be important for the partition of any enzyme by influencing the effect of phosphate concentration on the partition of proteins, although these experiments show that the partition coefficient of several enzymes is not much altered. The partition parameters allow the substitution of Dextran T‐500 fractions by crude dextran or unfractionated, slightly hydrolyzed fractions. Using crude dextrans the performance and technical realization of enzyme extraction processes are demonstrated for pullulanase from Klebsiella pneumoniae and formate dehydrogenase from Candida boidinii.Both enzymes were recovered in comparable high yields. The equipment performance was quite good, as indicated by the high throughput values of the separators employed. Especially when using nozzle separators for phase separation there is a better performance in comparison to the Dextran T‐500 fraction. No serious technical problems were encountered when replacing the expensive fractionated dextran with a crude dextran. In this way aqueous two‐phase systems containing dextran become more feasible for enzyme purification from an economic point of view. The price of about 1.30 German marks (DM) per liter for a useful phase system already appears acceptable for the production of valuable intracellular enzymes.