34 



VIRUSES 



By confining attention to the upper curve, one can see that a straight 

 line actually is obtained when the data are thus plotted, at least over the tem- 

 perature range of 60° to 76° C. From the slope of this line, the energy of ac- 

 tivation for the thermal denaturation of tobacco mosaic virus was calculated to 

 be 153»000 calories per mole. This value is significant because it is very highj 

 it is similar to the energies of activation for other protein denaturationa and 

 much higher than the energy of activation for most ordinary chemical reactions. 

 There is one more thing that must be observed on this figure. All of the data 

 fitting the lower line were obtained with virus solutions at an original concen- 

 tration of 6 mg. per cc., and those fitting the top line v/ere obtained with virus 

 at an original concentration of 3 ™g» per cc . These results, when transformed 

 from logs back to simple numbers, show that a virus solution of 3 nig. per cc , 

 initial concentration will denature with a specific reaction velocity about 

 twice that of a virus solution at an initial concentration of 6 mg. per cc. Now, 

 the specific reaction velocity k of any process, is supposed to be a constant 

 which is entirely independent of the initial concentration of the reactant . Hence 

 this observation constitutes an exceptional case and is, therefore, worth some 

 attention, because it must mean something. Later in this discuBsion, this mat- 

 ter will be considered more fully. At the present it should be pointed out that 

 this observation affords a chemical basis for the earlier observation of Price: 

 that the stability of heat of tobacco mosaic and other plant viruses decreases 

 with dilution of the virus. It is interesting to extrapolate the data of Fig- 

 ure 26 to room temperature to see how fast tobacco mosaic virus would denature. 

 When one does this, he finds that 30° C., log k = - 33«1?- Transforming to num- 

 bers, ic=4 X 10-15 min.-l at 30" C« This means that the virus should have a half 

 life * of around a billion years. 



It has been known for many years that some viruses can be destroyed by 

 subjecting them to extremely high pressures. In 19^1, Dow cooperated in some 

 experiments on the denaturation of tobacco mosaic virus at high pressures, it 

 was found that, when the virus was exposed to pressures between 5»000 and 10,000 

 atmospheres or kilograms/sq .cm. , it was transformed into an inactivated coaguliim. 

 Huclelc acid was split off in the process. The kinetics of the reaction at a 

 pressure of 7500 kilograms per square centimeter was studied in a little detail. 

 The results are shown in Figure 27. 



40 80 \2D 160 200 240 

 TIME IN MINUTES 



FIGURE 27 - LOG CONCEITTRATION OF TOBACCO MOSAIC VIRUS PROTEIK PLOTTED 

 AS A FimCTION OF TIME OP EXPOSURE TO PRESSURE OP 7^00 KILOGRAlIS/Sq.Cll. 

 AT 30° C. (M.A. Lauffer and R.B. Dow, J. Biol. Chem. 140, ?09 (1941) ). 



