276 



J. D. SMITH 



Fig. 4. Two alternative 1000-v. power supplies for the electrophoresis apparatus. 

 In circuit B the transformer output must be at least 440 v. r.m.s. at 60 ma. The metal 

 rectifiers are in pairs of 350 v. 60 ma. The series resistance in the transformer primary 

 circuit is 1000-5000 ohms rated at 200 ma. and may be replaced "with advantage by a 

 variable autotransformer. 



Under most conditions the movement due to endosmotic flow is neg- 

 ligible, but when the substances are placed near one end of the paper there 

 is an additional movement towards the opposite electrode which appears 

 to be largely due to the movement of buffer into the incompletely saturated 

 paper. In practice this is unimportant, but may be minimized by placing 

 the substances near the center of the paper. 



III. Applications of the Method 



1. Determination of Nucleic Acid Composition 



The ease with which adenylic, guanylic, cytidylic, and uridylic acids 

 may be separated bj^ paper electrophoresis leads to a simple method for 

 the determination of the quantitative purine and pyrimidine composition 

 of pentosenucleic acids (PNA), which has been developed by Davidson 

 et al.'''^'^^ The PNA (about 5 mg./ml.) is hydrolyzed to nucleotides in 



" J. N. Davidson and R. M. S. Smellie, Biochem. J. 52, 594 (1952). 



