PHYSICAL PROPERTIES OF NUCLEIC ACIDS 475 



still low did not correspond to the theoretical value for a tetranucleotide 

 (1300). In view of the degradation which must generally occur during the 

 isolation of pentose nucleic acids, it is doubtful whether the values recorded, 

 of which examples are given in Table Y, have any direct connection with 

 the molecular weight of the parent nucleic acid in the cell and can only 

 refer to a particular sample isolated in a certain way. Furthermore, in view 

 of the degradation, the determinations will, in general, have been carried 

 out on polydisperse solutions, and it is evident that an analysis for hetero- 

 geneity and a fractionation should be made prior to molecular weight 

 determinations. Delcambe*^ and Ghuysen^^ have carried out such analyses 

 by means of solubility measurements, and Bacher and Allen^^ have com- 

 bined solubility and sedimentation studies in order to characterize pentose 

 nucleic acids. 



High-molecular-weight (greater than 10^) nucleic acids have been ob- 

 tained from virus and, more recently, from a variety of different tissues 

 (85a, 85b, 85c). The highly polymerized ribonucleic acid obtained from 

 tobacco mosaic virus has been studied by Cohen and Stanley.*® The virus 

 nucleic acid was prepared by heat denaturation of the virus and had a 

 molecular weight of between 1.5 and 2.9 X 10\ This preparation was 

 heterogeneous, however, and decomposed spontaneously to give a nucleic 

 acid of molecular weight 5.9-7.0 X 10^ which possessed a higher degree of 

 homogeneity. From the original highly polymeric material, by treatment 

 with 5 % sodium hydroxide, a fairly homogeneous nucleic acid sample hav- 

 ing a molecular weight of 1.5 X 10^ was obtained. 



3. Acid-Base Properties 



The nucleotides, as has been shown, all possess characteristic acidic dis- 

 sociations owing to the presence of the primary and secondary phosphoric 

 acid groups, the amino group, or the — NH — CO^ — group in the molecule. 

 These groups again appear in the nucleic acids, and the analysis of the 

 electrometric titration curves yields information both as to the nature of 

 the internucleotide linkage and the macromolecular structure. 



a. Deoxypentose Nucleic Acids 



The early titration data on the deoxyribonucleic acid of thymus^"''' were conflict- 

 ing, the acid, in titration up to pH 8.0, being classified as pentabasic or tetrabasic by 



"L. Delcambe, Bull. soc. chim. Beiges 59, 508 (1950). 



88 J. M. Ghuysen, Bull. soc. chim. Beiges 59, 490 (1950). 



89 J. E. Bacher and F. W. Allen, J. Biol. Chem. 184, 511 (1950). 

 '"H. Steudel, Z. physiol. Chem. 77, 497 (1912). 



" R. Feulgen, Z. physiol. Chem. 104, 189 (1919). 



92 P. A. Levene and H. S. Simms, J. Biol. Chem. 65, 519 (1925). 



»» P. A. Levene and H. S. Simms, J. Biol. Chem. 70, 327 (1926). 



