32 



MICROSOMAL PARTICLES 



The agreement between the light-scattering molecular weight and that cal- 

 culated from sedimentation and viscosity data justifies the application of 

 the Mandelkern-Flory relation to the lower-molecular-weight samples listed in 

 the upper part of table 1. The molecular-weight dependence of these two quan- 

 tities can then be examined. This is done in figure 3, where the logarithms of 

 s° and [y\] are plotted against the logarithm molecular weight, yielding the 

 linear relations 



/=2.1xl0" 2 M 0A9 

 [n]=:6.2xl0- 4 M - 53 



This type of dependence is associated with homologous samples of linear, ran- 

 domly coiled polymer chains. These exponents are close to the limiting value 

 of 0.5 which is reached for chains having the maximum permissible extent of 

 coiling [7], So high a degree of coiling is unexpected in a highly charged poly- 

 electrolyte at the relatively low ionic strength used here and must be taken to 

 indicate that the intrachain attractions are strong enough to overcome the ex- 

 pansive electrostatic effect. 



Provided that RNA is a randomly coiled, single chain, we should expect the 

 relatively tight coiling to give way to a much more expanded coil in the ab- 

 sence of added electrolyte. This would be recognized by a much higher viscosity 

 and the further increase in the reduced specific viscosity upon dilution with 

 water, a behavior known as the electroviscous effect in polyelectrolyr.es. When 

 the RNA is transferred to aqueous solution (pH 5), its reduced specific 

 viscosity at 0.6 g/dl is found to be 0.85 and to increase strikingly upon dilution. 

 These results, shown in figure 4, clearly indicate the progressive expansion of the 



10000 



20,000 



40,000 



100,000 



Fig. 3. Logarithmic dependence of the sedimentation constant and intrinsic viscosity of 

 RNA upon the molecular weight. 



