29. DEOXYRIBONUCLEIC ACIDS AS MACROMOLECULES 19 



shape of the molecule, will then be a function of the intensity of the elec- 

 trostatic interaction; that is to say, of the concentration of the added 

 electrolyte. This can be easily observed in Fig. 7B which relates to a solu- 

 tion of flexible chains of polyvinylbutylpyridinium bromide (PVBPB) in 

 water or in salt solutions. Very important differences between the curves 

 in Fig. 7A and 7B may be observed. ' H 



First, there is a peak for rj sp /c as a function of c in the case of PVBPB, 

 which does not appear in DXA solutions. 



Second — and this is even more important — the extrapolated values [rj] 

 of 7? sp /c are, in the' first case, decreasing as the concentration of the salt 

 increases while they remain constant in the second case. This means that 

 the configuration of the DNA particles in solution does not change whether 

 or not their different parts undergo mutual repulsions. 



In conclusion, these particles have no internal mobility. They are stiff, 

 or rigid, bodies. This is the first result that we obtain from the application 

 of hydrodynamical methods. 



Other phenomena observed on DNA solutions, such as stream double 

 refraction 10 or structural viscosity, 1 which are connected to the orientation 

 of the particles in solution confirm this statement. 



However, in the case of stream double refraction, DXA seems to behave 

 as an intermediary between a quite rigid particle, such as tobacco mosaic 

 virus (TMV), and a quite flexible molecule, such as polystyrene (Fig. 8). 

 This could be interpreted along the lines of Cerf 's theory 1 as a slight flexi- 

 bility of the molecule. But a careful examination of the ultraviolet absorp- 

 tion of DXA in glycerol solutions shows that, at higher concentrations of 

 glycerol, there appears to be a slight denaturation of the molecule which 

 could be responsible for the observed flexibility. 



We must maintain the conclusion that DXA. particles very probably 

 possess rigid configurations. 



Perhaps it is of interest to note here that RNA, in contrast to DXA, 

 behaves as a quite flexible polyelectrolyte " as appears clearly from the 

 comparison of Fig. 7A and 7C. 



2. LiCxHT Scattering in DXA Solutions 



The study of light scattering in DXA solutions has been widely developed 

 in the last few years, and many of its conclusions have been discussed in 

 numerous papers. Only recently, however, has the validity of the interpre- 



13 J. Pouyet, Compt. rend. acad. set. 234, 152 (1952). 



M H. Eisenberg and J. Pouyet,/. Polymer. Sci. 13, 85 (1954). 



13 H. Schwander and R. Cerf, Heir. Chim. Acta 32, 2356 (1949). 



16 J. Pouyet, ./. chim. phys. 48, 161 (1951). 



17 R. Cerf, Fortschr. Hochpolym. Forsch. 1, 382 (1959). 



18 U. Z. Littauer and H. Eisenberg, Biochim. el Biophys. Acta 32, 320 (1959). 



