PURINES AND PYRIMIDINES 7 



In this manner, the deoxypentose nucleic acids of thymus, spleen, 

 liver, and also yeast were prepared. The corresponding compound 

 from tubercle bacilli was isolated via the nucleoprotein^o. The 

 procedures leading to the preparation of deoxypentose nucleic 

 acid from human sperm will soon be published^i. All deoxypen- 

 tose nucleic acids used in the analytical studies were prepared 

 as the sodium salts (in one case the potassium salt was used); 

 they were free of protein, highly polymerized, and formed ex- 

 tremely viscous solutions in water. They were homogeneous 

 electrophoretically and showed a high degree of monodispersity 

 in the ultracentrifuge. 



The procedure for the preparation of pentose nucleic acids 

 from animal tissues resembled, in its first stages, the method of 

 Clarke and Schryver-^. The details of the isolation procedures 

 and related experiments on yeast ribonucleic acid are as yet 

 unpublished. Commercial preparations of yeast ribonucleic acid 

 also were examined following purification. As has been men- 

 tioned before, the entire problem of the preparation and homo- 

 geneity of the pentose nucleic acids, and even of the occurrence 

 of only one type of pentose nucleic acid in the cell, urgently 

 requires re-examination. 



5. SEPARATION AND ESTIMATION OF PURINES AND PYRIMIDINES 



Owing to the very unpleasant solubility and polar characteristics 

 of the purines, the discovery of suitable solvent systems and the 

 development of methods for their quantitative separation and 

 estimation-^' ^^ presented a rather difficult problem in the solution 

 of which Dr. Ernst Vischer had an outstanding part. The pyrim- 

 idines proved somewhat easier to handle. The choice of the 

 solvent system for the chromatographic separation of purines and 

 pyrimidines will, of course, vary with the particular problem. The 

 efficiency of different solvent systems in effecting separation is 

 illustrated schematically in Fig. 1. Two of the solvent systems 

 listed there are suitable for the separation of the purines found 

 in nucleic acids, i.e., adenine and guanine, namely (1) n-butanol^ 



References p. 23 



