40 



VIRUSES 



Measurements were made at 0°C. and also at 4 5"^ C. The logarithir, of the reaction 

 velocity la plotted against the logarithm of the urea concentration for each 

 case. It can be seen that the data fall on straight lines, as required by the 

 theory. 



it may be recalled that the heat denaturation of tobacco nosaic virus var- 

 ied, in contradiction to all accepted rules, with the reciprocal of the initial 

 virus concentration. A fairly extensive study of the effect of initial con- 

 centration of virus in the urea denaturation was accordingly carried out. In 

 Figure 32 it can be seen that as the initial concentration of virus is decreased, 

 the specific reaction rate for the denaturation increases. This confinrs the 

 behavior for thermal denaturation. 



CONC - MG/CC. 



FIGURE 32 - SPECIFIC REACTION VELOCITY DT VITJ.-^ OF THE iJREA 

 DENATURATION OF TOBACCO MOSAIC VIRUS PROTEIN PLOTTED AS A FUNCT- 

 ION OF ITIITIAL VIRUS CONCENTRATION. (MJV. lauffer, J. Amer. Chens. 

 Soc. 65, 1793 (1943) ). 



If equation (7) is re-examined, it can be seen that the reaction velocity cons- 

 tant is proportional to, among other things, the ratio of the activity coef- 

 ficient of the intact virus to the activity coefficient of the activated virus. 

 The equation applying to this case would be more complicated than (7), but the 

 principle is the asune . it is well known that the activity coefficients of many 

 materials are dependent upon their own concentration. In some cases the mech- 

 anism by which the activity coefficient is influenced by concentration is well 

 understood. In other cases this mechanise is not understood, it is conceivable 

 that the activity coefficient ratio is in some way a function of the initial 

 concentration of virus. Such a relationship could account for the variation of 

 the reaction rate with Initial virus concentration, it would constitute a for- 

 mal thermodynamic rationalization of the process. However, it would constitute 

 self-deception to pretend that this really constitutes an explanation of what 



