290 M. Westergaard 



Giles, N. H., Jr. (1951). Cold Spr. Harb. Symp. quant. Biol, 10, 283. 

 GoLDSCHMiDT, R. (1935). Z. indukt. Abstamm.-u. VererbLehre, 69, 38. 

 Jensen, K. A., Kirk, I., Kolmark, G., and Westergaard, M. (1951). 



Cold Spr. Harb. Symp. quant. Biol., 16, 245. 

 K0LMARK, G. (1956). C. R. Lab. Carlsberg. Ser. physiol., 26, 204. 

 K0LMARK, G., and Westergaard, M. (1955). Hereditas, Lund., 39, 



209. 

 Landauer, W. (1954). J. Cell. comp. Physiol, 43, suppl. 1, 261. 

 Levan, a. (1951). Cold Spr. Harb. Symp. quant. Biol., 16, 233. 

 Mitchell, M. B., Mitchell, H. K., and Tissieres, A. (1953). Proc. 



nat. Acad. Sci., Wash., 39, 606. 

 Nachtsheim, H. (1950). Arch. Klaus-Stift. VererbForsch., 25, 566. 

 Provasoli, L., Hutner, S. H., and Pintner, I. J. (1951). Cold. Spr. 



Harb. Symp. quant. Biol., 16, 113. 

 Rapoport, I. A. (1947). Amer. Nat., 81, 30. 

 Sevag, M. G., Reid, R. D., and Reynolds, D. E., Ed. (1955). In 



Origins of Resistance to Toxic Agents, p. 423. New York : 



Academic Press. 

 Spiegelman, S., Halvorson, H. O., and Ben-Ishai, R. (1955). Iti 



Amino Acid Metabolism, p. 124. Baltimore; Johns Hopkins Press. 

 Westergaard, M. (1957). Chemical Mutagenesis and the Concept of 



the Gene, in press. 

 Wilson, G. B. (1950). J. Hered., 41, 227. 



DISCUSSION 



Alexander: Haddow has compared the cytotoxic effects of CB. 1506 

 (chloroethyl methanesulphonate, CiCH2.CH2.OSO2.CH3) and CB. 1528 

 (ethyl methanesulphonate, CH3.CH2.OSO2.CH3), using the growth of 

 the implanted Walker carcinoma, and found that CB. 1506 has a much 

 higher activity than CB. 1528. As a working hypothesis, it has been 

 suggested that CB. 1506 becomes activated in vivo by reaction with 

 cysteine to form a one-armed sulphur mustard : 



NH2 



CICH2 . CH2 . SCH2 . CH2 . CH 



I 

 COOH 



Do you consider it possible that such a reaction may also occur in youi 

 plant system? Our reason for believing that it may be necessary to 

 convert CB. 1506 metabolically into a more active compound is that the 

 chlorine atom in CB. 1506 is extremely unreactive, while in the postu- 

 lated cysteine derivative it would be highly active. 



Westergaard: Yes, I should think so. One possibility is that CB. 1506 

 may act in two different ways. It may form an epoxide, and epoxides 

 are exceedingly efficient in inducing adenine reversions, whereas CB. 

 1528 only acts as an ethylating agent. The inositolless strain which we 

 use likes everything which is able to ethylate and nothing else, which is 

 very surprising. We cannot account for this at present. 



