INACTIVATION OF VIRUSES 407 



mechanism, causing an initial activation of tlie reactive sites in a maimer 

 similar to that effected by L-tryptophan; fm-ther treatment is followed by 

 inactivation of the same sites. 



Bawden and Pirie (1940b) examined several other denatm-irig agents and 

 found them to have effects a2:)parently similar to those of urea. The remark- 

 able temperature dependence of the reaction rate seems to be a unique char- 

 acteristic of urea, however. Of the substances tested, including guanidine, 

 urethane, pyridine, phenol, salicylic, benzoic, and hippuric acid, most 

 seemed to split off RNA from rod-shaped, but not from spherical plant 

 viruses; they were usually active at much lower concentration levels than 

 urea. SDS was also tested and found to differ from the others by giving water- 

 soluble products and also by releasing RNA from tomato bushy stunt virus. 

 Reports concerning the effect of aniline are somewhat controversial; Lauffer 

 (1938) could not demonstrate any inactivation of TMV after 10 minutes 

 exposure to 50 % aniline in glycerol; Bawden and Pirie observed an immedi- 

 ate reduction in infectivity of 80 to 90 % which, however, did not show any 

 further progress even after 4 hours. Subsequently, Lauffer and Robinson 

 (1949) reported that different strains of virus behaved differently in this 

 respect. 



As already mentioned, cautious treatment with denaturing agents like 

 phenol (Gierer and Schranmi, 1956) or SDS (Fraenkel-Conrat and Williams, 

 1955) might give a protein-free virus nucleic acid retaining a considerable 

 activity. Obviously, protein denaturation per se is not directly responsible 

 for the inactivation observed. The fact that inactivation was found to precede 

 demonstrable denaturation also seems to exclude the possibility of a purely 

 indirect effect, i.e., by exposure of the labile nucleic acid deprived of its pro- 

 tecting coat. For the time being, the question of the mechanism of inactiva- 

 tion must be left open. 



D. Oxidizing Agents 



1. General Aspects 



Oxidation of organic material may, apart from the introduction of oxygen 

 into the molecule, result in dehydrogenation, deamination, opening of ring 

 structures, or formation of new rings (for a review of oxidation of proteins 

 see Herriott, 1947). All these reactions may lead to breakage of hydrogen 

 bonds. Therefore, oxidation, carried beyond certain limits, wOl almost in- 

 variably cause denaturation. Biologically active proteins, e.g., enzymes, may 

 be inactivated by a cautious oxidation, but the reaction is often reversible, 

 provided no denaturation has occurred. Reports of similar reversible inactiva- 

 tion of viruses (Perdrau, 1931), must, however, be viewed with some doubt. 

 Zamenhof et al. (1953) foimd that the Hemophilus transforming principle 



