36 



per-Ake albertsson 



nucleic acids collected at the interface. This part was included in the 

 bottom phase and thus the K^ values given in Table II are not strictly 

 partition coefficients. As may be seen in Table II, the larger the sedimen- 

 tation constant the smaller the tendency for the nucleic acids to partition 

 in favour of the top phase. 



Most proteins in the native state partition in favour of the lower phase 

 of the dextran methylcellulose system and the partition coefficient is 



T2 DMA 



Thi^mus DNA o 



o S-RNA 



J I 1__J I I 1 1 I L 



lO 



20 



30 



■^ 



20, ^ 



Fig. 2. Relation between the "partition coefficient", K^, and the sedimenta- 

 tion constant, S-.q, for a number of nucleic acid preparations. The data of Table II 

 are plotted in this figure. 



little influenced by the electrolyte composition. Thus, if the partition is 

 carried out in the presence of a o-oi m buff^er and an excess (o-i m) of 

 NaCl, the partition coefficient is constant over a wide pH range ; see Fig. 3, 

 where an experiment with human serum albumin is recorded [3]. Below 

 pH 4-5, however, the K value increases and even becomes greater than 

 unity, indicating that the protein has more affinity for the top phase at 

 acid pH values. It is interesting to compare this result with the viscosity 

 and optical rotation of serum albumin as a function of pH. Thus there is 



