34 per-Ake albertsson 



low molecular weight phase systems. Due to the presence of the polymers 

 in the phases, their viscosities are relatively high. The time of phase 

 separation is comparatively long for polymer two-phase systems; varying 

 from about 5 minutes to i day. Both non-ionic polymers and poly- 

 electrolytes may be used for the construction of a two-phase system [3]. 

 By varying the molecular weight, the number of non-polar groups, or 

 the number of charged groups on the polymers, a large number of phase 

 systems having highly diversified properties may be obtained. The phase 

 systems may be complemented by adding low molecular weight sub- 

 stances, such as sucrose or electrolytes, to achieve a suitable environment 

 for biological material. 



Partition of proteins, nucleic acids, and viruses 



The partitioning of a particle in a two-phase system depends mainly 

 on its surface properties including the area and the chemical properties 

 of the outer layer of the particle. 



The partition coefficients of some proteins and viruses have been 

 measured in a two-phase system of dextran and methylcellulose [3, 5] and 



TABLE I 



The Partition Coefficient, K, and the Surface Area of a Number of Virus 



Particles and Protein Molecules in a Two-Phase System of Dextran and 



Methylcellulose at 4'.* 



Data from refs. [3] and [5]. 



the results are given in Table I together with the surface areas of the 

 partitioned particles, calculated from their form and dimensions as 

 determined with the electron microscope. As may be seen in Table I, all 

 particles favour the bottom phase and the partition coefficient becomes 

 smaller the larger the particle size. In Fig. i, the log K values are plotted 

 against the particle surface area; it can be seen that the points lie around a 



* {K = concentration in top phase/concentration in bottom phase.) 



