980 7. MEKCURIALS 



but there appears to be a small resistant fraction which remains infectious 

 over several days (Krueger and Baldwin, 1934). Similar kinetics of inactiva- 

 tion have been reported by Moriyama and Ohashi (1941) for E. coli phage, 

 and by Allison (1962) for fowl plague and vaccinia viruses. 



The mercurials usually do not destroy the viruses or produce irreversible 

 structural changes in them, since reactivation with thiols has been observed 

 with staphylococcus phage (Wahl, 1939), influenza virus (Klein et at., 1948; 

 Perez et al., 1949), psittacosis virus (Burney and Golub, 1948), vaccinia 

 virus (Kaplan, 1959; Allison, 1962), streptococcal phage (Kessler and 

 Krause, 1963), and various enteroviruses (Choppin and Philipson, 1961). The 

 results of Krueger and Baldwin (1933, 1934) are particularly impressive; 

 reactivation with sulfide occurred even after exposure of phage to around 

 100 mM Hg++ for 9 days at 22o. It is remarkable that viruses, like certain 

 enzymes, can be reactivated readily with thiols (especially dimercaprol) 

 although no reactivation occurs by washing or dilution. Dimercaprol is 

 able to reactivate influenza virus in vivo when injected after the treated 

 virus in animals (Klein et al., 1948) or chick embryos (Perez et al., 1949). 



The reactivation with thiols does not prove that the mercurials react 

 with virus SH groups, as has been concluded, but there is evidence for the 

 importance of SH groups. The relative resistance of tobacco mosaic virus 

 to the mercurials is probably due to the unavailability of the SH groups, 

 since Anson and Stanley (1941) showed that p-MB reacts with all the SH 

 groups of denatured virus but does not inactivate native virus. Some steric 

 factor preventing reaction with p-MB was postulated by Fraenkel-Conrat 

 (1959), since MM reacts stoichiometrically in a 1:1 ratio with the SH 

 groups. The restriction may be imposed by hydrogen bonding to adjacent 

 groups. Some plant viruses are structurally altered by mercurials. Solutions 

 of potato virus X lose their flow birefringence when treated with p-MB, and 

 sedimentation studies indicate disintegration into subunits (Reichmann and 

 Hatt, 1961). It was concluded that the SH groups occur near the linkage 

 sites holding the units together, rather than participating in the linkage, 

 and that the bulky p-MB molecule splits the links. Turnip yellow mosaic 

 virus is also split into subunits by p-MB, and RNA is liberated simultane- 

 ously (Kaper and Houwing, 1962 a). The artificial top component (empty 

 virus protein shells) binds 645-660 molecules of mercurial per particle. As 

 structural changes occur, new SH groups are unmasked and react with 

 p-MB (Kaper and Houwing, 1962 b). Finally, one must consider the reac- 

 tion of mercurials with the nucleic acid components of the viruses, since 

 such complexes have been established (Katz, 1962). Tobacco mosaic virus 

 RNA complexes with Hg++ (Katz and Santilli, 1962 b) but much of the 

 infectivity remains in this case, although retention of specific infectivity 

 was not demonstrated (Katz and Santilli, 1962 a). 



We shall now inquire into the particular phases of virus multiplication 



