Enhanced discrimination in the partition of proteins by aqueous polymer two-phase systems

Aqueous polymer two-phase systems containing dextran T-500 and PEG 4000 can be prepared which are biphasic below 18 degrees C and monophasic at higher temperatures. Both liganded and unliganded forms of glutamate dehydrogenase and troponin, which have similar partition coefficients if the protein is added to a two-phase system at 4 degrees C, have widely differing partition coefficients if added to the same system in the monophasic state at 20 degrees C and subsequently cooled to 4 degrees C.