Partition of Macromolecules in 

 Aqueous Two-Phase Systems 



Per-Ake Albertsson 

 Institute of Biochemistry, Uppsala, Sweden 



Separation of substances by partition between two immiscible solvents 

 is one of the most frequently used methods in organic chemistry; in 

 inorganic chemistry, partition has also been widely used both for prepara- 

 tive and anahtical purposes. I\Iany biochemical substances, such as 

 polypeptides and even proteins, have also been studied by partition 

 methods, for example countercurrent distribution [i, 2]. 



One of the advantages of partition between two liquid phases is that 

 there is generally a greater possibility of obtaining a state of equilibrium 

 between two liquid phases than between a solid and a liquid phase. This 

 is particularlv so when macromolecules are involved. It would be of 

 great value if partition methods could also be applied to very high molecular 

 weight macromolecules of biological origin such as proteins, highly 

 polymerized nucleic acids, viruses, and cell particles. In recent years we 

 have studied this possibility in Uppsala and the present paper will describe 

 some experiments and a summary of the results obtained. A monograph [3] 

 dealing with the theoretical background and experimental details has 

 recently been published. 



Polymer two-phase systems 



In order to partition successfully biochemical macromolecules one 

 cannot usually use conventional two-phase systems containing an organic 

 solvent since this may cause denaturation. Instead a number of polymer 

 two-phase systems, obtained by mixing aqueous solution of two ditferent 

 polymers, have been used. It is a general phenomenon [4] that when 

 polymer solutions are mixed they give rise to two liquid phases, one phase 

 containing one polymer and the other phase the other polymer; both 

 phases have a high water content (85 99"o). Two aqueous phases in 

 equilibrium are thus obtained. The ditference in composition between the 

 phases is comparatively small; the interfacial tension, the differences 

 between the refractive indices and the densities of the two phases are 

 therefore much smaller for polymer phase systems than for conventional, 



