29. DEOXYRIBONUCLEIC ACIDS AS MACROMOLECULES 33 



dally by Butler and his co-workers, in order to obtain some significant re- 

 sults in the present situation. 



The general idea is to get rid of the dispersion of the S values by consider- 

 ing only one value *So , which corresponds to the maximum of the distribu- 

 tion curve (/{ S). This So value is the abscissa of the inflexion point of the 

 g( S) curve ( cf. Fig. 156). Each sample then is characterized by [77] and So . 

 It is assumed that all particles of the same molecular weight have the same 

 [77I and the same N„ or, in other words, that there exist such definite func- 

 tion as N„( .1/ ) and MU/) . These functions are supposed to be the same as 

 those which have been observed to be valid in the general case of high poly- 

 mer solutions, for instance box and Flory's equations which, by a proper 

 combination ° lead to the so-called Mandelkern equation 



S [r)] 9I170 _ 

 -l/2/3 (1 _ FspPo ) 



where ft is an empirical constant. In comparing the DXA particle with a 

 high polymer coil, (S is chosen to be equal to 2.6 X 10 . Then all is ready 

 for the calculation of M from So and [77]. 



Butler" 4 has found that, for a series of five different preparations coming 

 from calf thymus, the molecular weights thus calculated lay between 8.5 X 

 10 h and 10.8 X K)\ These values are of the same order of magnitude as 

 those which have been found for M v . (group I ). However it has to be em- 

 phasized that the author has measured the light-scattering molecular 

 weights for the same samples and has found them to be between 3 and 4 

 million. He concludes that there is no agreement between M w and M vS 

 values. On the contrary, a good agreement of the same quantities is found 

 for X-ray-degraded samples, for which the common value of M w is some- 

 what under 4 X 10 6 . 



IV. Conclusions 



The general conclusion to be drawn from the brief survey attempted here 

 is that the situation still is rather confused. On the one hand, we have shown 

 that light-scattering measurements, at least solar as the molecular weight 

 of DXA particles is concerned., are suspect, and, on the other, that the use of 

 hydrodynamical methods relies on assumptions (Section 111,3,6) whose 

 validity is very difficult to accept or, at any rate, to estimate. 



Despite our necessarily critical attitude the following conclusions may, 

 however, be proposed: 



(a) The character of the particles in dilute solution depends in general 



24 J. A. V. Butler, I). J. R. Laurence, A. B. Robins, K. Y. Shooter. Prcc. Roy. Soc. 



A250, 1 (1959). 

 26 L. Mandelkern, P. J. Flory, W. R. Krigbaum, and H. A. Scheraga, ./. Chem. 



Phys. 20, 1392 (1952). 



