29. DEOXYRIBONUCLEIC ACIDS AS MACROMOLECULES 



29 



and we shall limit our discussion to the case of samples MAV and AMJi 

 which, as we have seen, had been prepared without any preliminary precipi- 

 tation of the DNA. 



1. As we have already mentioned, the c/K curves, for samples not 

 treated with chymotrypsin, depend on the concentration of NaCl in the 

 solution. This effect disappears almost completely after treatment with the 

 enzyme (Fig. 12A and B). 



2. Within the limits of the precision of the experiments, it seems that 

 these curves admit a linear asymptote as it appears in Fig. 12A and B and 

 more clearly in Fig. 13 relative to sample CV71. 



3. Thus we may assume that the DNA particles behave like rods, or like 

 large zigzag chains, and the slope of the asymptote gives the value of M/L. 



For MAV and AMJi — without previous treatment with chymotrypsin — 

 the values of M/L depend on the concentration of NaCl in the solution. 

 Figure 14 shows that M/L has a maximum for a concentration of 0.15 

 molar NaCl just as has been observed for M w . M/L is the same for the 

 two samples at a concentration of 1 molar NaCl, and its value is 250 (mole 

 per A.). The effect of the salt concentration disappears if the sample have 

 been treated by chymotrypsin and the constant value of M/L lies between 

 200 and 220. It is important to note that the M/L values are quite com- 

 patible, within the range of experimental errors, with the theoretical value 



Sin 9/ 2 

 Fig. 13. Another example (sample CV71 in 1 molar NaCl) of linear variation of 

 c/K as a function of sin 0/2 for large values of 9. 



