THERMAL INACTIVATION OF VIRUSES 111 



are A//* = ^25,300 calories/mole and AS* = —7.4 calories mole/ 

 degree. Some unpublished experiments by the author and 

 Dimond on i)urified, dry TMV give MI^ = 27,000 and A*S* = 0. 

 The dry virus is, therefore, characterized by a low or zero 

 entropy of activation and a moderate value of AH^. The low 

 entropy is characteristic of dry substances (Pollard, 1951). 



The wet inactivation yields two sets of figures. Below about 

 85° C, the reaction constant varies relatively slowly with 

 temperature, yielding AH^ = 40,000 and AS* = 18 in some 

 experiments made by the author and Dimond and which sub- 

 stantially agree with the data obtained by Price. Above about 

 85° C, the temperature dependence rises markedly. Price's 

 figures for the undiluted virus corres})ond to a A/7* of 195,000 

 carlories/ mole and a AS* of 410, roughly. The very much larger 

 value of AS* above 85° C speaks for a completely different 

 process taking place. Lauffer and Price (1941) studied the 

 denaturation of TMV with thermal action. TMV behaves in a 

 rather interesting manner at high tem])eratures. The small frac- 

 tion of nucleic acid is removed from the protein binding, the 

 protein becomes denatured, and goes out of solution. The rate 

 processes for this were carefully measured by Lauffer and Price 

 (1941) with the result that, at pU 6.8, the values of 153,000 for 

 A//* and 370 for AS* were obtained. 



It is thus clear that infectivity and protein denaturation do 

 not necessarily go together. The latter is characterized by very 

 large entropies of activation, and the former by lower values. 

 If the temperature is high enough, the thermal action on the 

 protein part will stop the virus from functioning faster than will 

 the other process, whatever it may be, which was causing the 

 infectivity loss. It will be seen later that the loss of serological 

 affinity follows a high-entropy type of kinetics and so is presuma- 

 bly related to protein denaturation. 



The two processes are plotted in Fig. 4.4, in which the rate 

 constants for TMV inactivation and denaturation are plotted 

 versus temperature. The two separate processes of denaturation 

 and infectivity loss are seen to combine in the one curve as 

 measured by Price. It is tempting to suppose that the slow 



