PHYSICAL PROPERTIES OF NUCLEIC ACIDS 473 



TABLE IV 

 Molecular weight and Dimensions of Deoxypentose Nucleate Ion in 



0.2 M NaCl 



using the light-scattering method. Earher studies by Oster"^ and Smith and 

 Sheffer^^ had shown that nucleic acid solutions were suitable for such 

 studies, and a value of the molecular weight of 4.4 X 10^ was obtained by 

 Smith and Sheffer. The values obtained by Doty and Bunce^^ for three 

 different samples of sodium deoxypentose nucleate are given in Table IV. 

 The sample of Gulland et al?^ was identical with that examined by Cecil and 

 Ogston^" and shows that the light-scattering method yields a value approxi- 

 mately four times as great as that obtained by sedimentation. This dis- 

 crepancy may be due in part to the possibility that the scattering envelope 

 is not identical with the sedimenting unit, but is also very probably due to 

 the value of the sedimentation coefficient obtained by existing extrapola- 

 tion methods being too low. More recently, Reichmann et al.''^ have ob- 

 tained the value of 7.7 X 10^ for the molecular weight of a new sample, 

 prepared by the method of Signer,^'- and Katz^^ has recorded a value of 8.0 

 X 10^ for a similar preparation. 



Lower estimates of the molecular weight have been obtained by Jungner et alJ^-''^ 

 from dielectric dispersion measurements (1.2-8.4 X 10^). For the Gulland prepara- 

 tion'" the value 6.1 X 10* was obtained (compared with 1.3 X 10* by sedimentation 

 and difTusion*"'" and 4 X 10* by light-scattering*' methods). The dielectric molecu- 

 lar weight represents the weight of individual units orienting independently in an 

 electric field. Whether these units represent a single nucleic acid molecule or sections 

 of a larger molecule is difficult to decide at present. Jungner et al. assume the former 

 possibility to be correct and consider that the sedimentation and light-scattering 

 methods give the molecular weight of aggregates of molecules. This point was, how- 

 ever, carefully investigated by Doty and Bunce," who from the linearity of the zero- 

 angle curve conclude that no aggregation occurs. It would therefore appear more 

 probable that the dielectric molecular weight is not the true molecular weight, but 

 that of an orienting unit. 



6' P. Doty and B. Bunce, J. Am. Chem. Soc. 74, 5029 (1952). 



*» G. Oster, Trans. Faraday Soc. 46, 794 (1950). 



69 D. B. Smith and H. Sheffer, Can. J. Research B28, 96 (1950). 



'» J. M. Gulland, D. O. Jordan, and C. J. Threlfall, J. Chem. Soc. 1947, 1129. 



■"■ M. E. Reichmann, R. Varin, and P. Doty, J. Am. Chem. Soc. 74, 3203 (1952). 



'2 R. Signer and H. Schwander, Helv. Chim. Acta 32, 853 (1949). 



" S. Katz, J. Am. Chem. Soc. 74, 2238 (1952). 



