116 MUTATIONS 



MgCL, and ZnClo. Tests involving 18 Na salts indicated that the 

 effect of washing depends on the concentration of Na ions in the wash- 

 ing solution rather than on its pH. The mutagenicity of MnCU was 

 tested under several other conditions. As was mentioned by Dr. Auer- 

 bach, the explanation given for the mode of action of MnCL is that 

 in some unspecific fashion it affects the metabolic activity of bacterial 

 cells in such a way as to make the gene systems more unstable than 

 they otherwise are. 



Neel: Is there any other chemical whose effects are so modified by 

 your pre- and posttreatment as this one? 



Demerec: From among the large number of chemicals tested, only 

 MnClo and a few related compounds were found to be highly muta- 

 genic and reactive to pretreatment (16). They were: manganous 

 sulphate, nitrate and acetate, and ferrous chloride and sulfate. They 

 did not include manganous lactate, ferric chloride or sulfate, or several 

 stannous, cerous, cobaltous, and nickelous salts. 



Goldstein: Were experiments ever done with posttreatment with 

 a chelating agent like EDTA? 



Demerec: No. 



Lederberg: On the mechanism of action of manganous ion, I think 

 you yourself suggested the possibility, perhaps even the probability, 

 that this is functioning in an intermediate. Peroxide plus ferrous iron 

 is a very active oxidizing agent, and I would be surprised if this weren't 

 true to some extent with manganese as well. Has this been clarified at 

 all? 



Demerec: No. You see, this work was done before it was known that 

 peroxides were potent mutagens and that they may be responsible for 

 the mutagenic effect of ultraviolet radiation. 



Auerbach: But it is such a specific mutagen. 



Lederberg: That may be a matter of being in the right place in the 

 cell. Even posttreatment effects may have something to do with having 

 localized it. 



Auerbach: No, I mean in the sense that only certain strains react 

 with it, even in E. coll. 



Lederberg: Presumably, it has to complex with something in the 

 cell or it won't stay there. 



Auerbach: But wouldn't you expect that this might happen in every 

 cell, not only in very special ones? 



Lederberg: I'm sure that if you fixed manganous iron or ferrous 

 iron with hydrogen peroxide, you would get tremendous lethal effects. 



Zamenhoj: No, not manganous. Ferrous iron reacts strongly (86, 91) 

 but manganous does not. 



