Three-phase affinity partitioning of proteins.

Three-phase partitioning is an elegant way to separate proteins directly from even the large volumes of crude suspensions. It was found that interfacing it with a metal-affinity-based step makes the technique highly selective. As "proof of the concept," soybean trypsin inhibitor was purified 13-fold with 72% recovery. As recombinant proteins (via their polyhistidine tags) and many other naturally occurring proteins are often purified by immobilized metal ion affinity chromatography, the technique described here should prove valuable in purifying biotechnologically important proteins at a large scale.