386 S. GARD AND O. MAAL0E 



Such low activation energies are usually only found for dried viruses: for 

 TMV, Price (1940) obtained a AH value of about 24,000 cal./mo]e,as opposed 

 to the high values obtained for wet virus (see above); and Pollard and Eeaume 

 (1951) found even lower values for the phages Tl, T3, and T7. The AS* 

 values, which in wet preparations run between 100 and 1000, had dropped to 

 around zero. As pointed out by Pollard (1953), the entropy of activation, in 

 the wet as well as in the dry state, is not correlated with the size of the 

 virus; this suggests that inactivation involves changes in small regions rather 

 than uniform denaturation of the virus protein. 



For heat denaturation (insolubilization) of TMV protein, at a given virus 

 concentration and pH, Lauffer and Price (1940) found a single, weU-charac- 

 terized AH value. Boyd and Eberl (1948) attempted to interpret the data of 

 Lauffer and Price in terms of the number of H bonds which may have to be 

 broken simultaneously to initiate denaturation; their figure is 25-30 out of 

 more than 10,000. Normally, protein and KNA become separated when TMV 

 is heated but, at very low salt concentrations, the virus rod is transformed 

 into a ball in which the RNA is trapped (Hart, 1956b). This transformation 

 seems to require an activation energy similar to the one found for denatura- 

 tion of TMV protein. 



As in radiation experiments, the hemagglutinating activity is much more 

 resistant than infectivity. The activation energy is of the order of 100,000 

 cal./mole, but the reaction rate was found to depend in a complicated manner 

 on the initial virus concentration (Lauffer and Carnelly, 1945; Lauffer and 

 Scott, 1946; Scott and Lauffer, 1946a). Similar high values have been re- 

 ported by Woese (1956) for the heat of activation of a number of influenza 

 A strauis, for one B strain, and for Newcastle, mumps, and swine influenza 

 viruses. The A strains were characterized by identical high AH* values 

 (170,000 cal./mole); for the other viruses, the values ranged between 100,000 

 and 340,000 cal./mole. 



PoUard and Setlow (1953) followed the loss of the ability of phage Tl to 

 combine with antibody. In the wet as well as in the dry state, the AH* and 

 AS* values were considerably higher than had previously been measured for 

 inactivation. The low AS* values, characteristic of dry preparations, suggest 

 that inactivation may occur without profound denaturation and therefore 

 without loss of serological afiinity and antigenicity (Pollard and Reaume, 1951). 



A few observations suggest that heat treatment of a virus may sensitize 

 it in a manner analogous to what was found m X-ray and UV experiments. 

 Thus, Smith and Kreuger (1952a,b) have reported that a vibrio phage, when 

 heated for a short time, becomes permanently sensitive to cold shock; Hart 

 (1955b) has shown that heating in the presence of smaU amounts of the deter- 

 gent Duponol C sensitized TMV to the action of RNAase. Subsequent inacti- 

 vation occurs without removal of measurable amounts of RNA. 



