DISINTEGRATION OF VIRUSES 35 



It was found that, when the logarithm of the amount of nitrogen in the super- 

 natent fluid, which is proportional to the amount of virus remaining undenatured 

 is plotted against the time, a straight line is obtained. This would indicate 

 that the pressure denaturation of tobacco mosaic virus protein is a reaction of 

 the first order. From the data obtained, one can calculate that the specific 

 reaction rate at 30° C. is 7.45 x 10"3 min."^. ''^^ logarithm to the base e of 

 that figure is a -4.9. * * It was estimated previously that, 



at 30° ^' a't s pressure of 1 atmosphere or about 1 kilogrsun/sQ .cm., the extra- 

 polated value of the reaction rate is ^ ^ lO""'"^* '^'^"^ 'the value at a pressure 

 of 7f500 kg/sq.cm. is about lo^^ as fast. 



It might be asked, by what mechanism does an increase in pressure cause 

 such a tremendous increase in rate? If one examines the theory again, one can 

 see that an increase in pressure might cause a shift in the equilibrium between 

 normal virus and activated virus. If the activated virus particle has a slight- 

 ly lower molecular volume than the normal particle, then an increase in pressure 

 would shift the equilibrium toward more activated virus. This would speed up 

 the reaction. This idea can be treated quantitatively through the use of some 

 of the results of thermodynamics. Students of elementary thermodynamics learn 

 that the following equation holds: 



y^^'-i =A7 (12) 



T 



ZjV is the change in partial molar volume accompanying a reaction. By combining 

 (7)t (fl). and (12), one obtains 



d In K _ Av. d In k ,,,, 



dP "RT ~ dP ^^^' 



If the data described above are substituted into eqviation (13)f a value of 

 -97»000 cc. is obtained for Av. This means that in the process of passing from 

 the normal state to the activated state, there is a decrease in volume of 97fOOO 

 cc. per mole. ITie molecular weight of tobacco virus is about 3O-35»0OO,0O0 grajns 

 and the specific volume is about 0.75 cc/gram. Therefore, the molar volume of 

 the virus is about 2^,000,000 cc . The shrinkage in passing to the activated 

 state is thus about 1 part in 2^0, or 0.4^. 



When tobacco mosaic virus is dissolved in a 6 molar solution of urea buf- 

 fered to pH 7 with phosphate buffer, many changes take place simultaneously, as 

 illustrated in Figure 28. Virus infectivity is lost. The virus protein with a 

 sedimentation constant of ^ge ^ 10"^3 is gradually converted into components 

 with sedimentation constants ranging from 50 to 2 x 10"13« J-hese 



smaller particles, although completely soluble in urea, come 



out of solution when the urea concentration is reduced by dilution or by dialy- 

 sis . The precipitated material is free of nucleic acid. 



