ALEXANDER HOLLAENDER AND C. O. DOUDNEY 



A number of other conditions involving cysteamine protection of E. coli 

 have been tested. Cysteamine-protected, irradiated E. coli suspended in 

 yeast extract for only 15 minutes, then removed by centrifugation, washed 

 carefully, and plated out on minimal agar plates recover as if they were 

 plated on yeast extract plates. In other words, the stimulus to recovery 

 from yeast extract is transferred to the bacteria within a few minutes. 

 Another test was made to see whether the cysteamine in the suspending 

 medium is important or whether the cysteamine goes into the bacterium 

 and exerts its protective effect inside the cell. For this purpose, bacteria 

 were kept in cysteamine for 30 minutes, then washed off with salt solution 

 and resuspended before irradiation. The data show that the cysteamine 

 must have exerted its effect inside the bacterial cell since, in spite of careful 

 washing, the cells remain highly resistant to the lethal effects of radiation 

 as compared to the control. 



The problem of mechanism of protection has also been approached by 

 studying the effectiveness of cysteamine modified structurally in various 

 ways^. When both the thiol and amine groups were covered with other 

 groups, it was found that the data obtained with bacteria in regard to 

 derivatives of cysteamine do not necessarily apply to the protection of mice. 

 For instance, S,[i-aminoethylisothiouronium bromide HBr protects mice 

 exceedingly well against the lethal effects of irradiation. As a matter of 

 fact, this compound has many advantages over cysteamine for protection 

 of mice. However, this compound actually increases the killing effect of 

 radiation on bacteria. For example, at 60 kr only about 1/100 as many 

 cells survive in the presence of this compound as in its absence. One could 

 speculate that actively metabolizing mammalian tissue could break this 

 compound down into a form which is protective. E. coli in the resting-cell 

 state, as we study them {i.e. in a salt solution at 2°C), are not able to do 

 this. Perhaps this compound in its intact form competes in some manner 

 with compounds or for sites responsible for part of the innate radiation 

 resistance of the cell. In contrast, the acetylated derivatives of cysteamine 

 offer small protection for mice. However, both the S-acetyl and N-acetyl 

 derivatives of cysteamine will protect E. coli to a very high level. There is 

 no obvious reason why these latter two compounds should not protect mice 

 as well as the thiouronium compound. The N,S-diacetyl derivative of 

 cysteamine will protect E. coli only if incubated with the organisms at 37° C 

 for 30 minutes prior to irradiation. It is apparent that we cannot conclude 

 from experiments with bacteria that the results are directly applicable to 

 mammals. We believe, however, that a fuller understanding of the details 

 of the mechanism of cysteamine protection in bacteria will aid in defining 

 both the pre- and post-irradiation conditions which may lead to more 

 successful control of radiation damage to mammals. 



REFERENCES 



^ Stapleton, G. E., Sbarra, A.J. and Hollaender, A. 1955, to be published, 



2 Stapleton, G. E., Billen, D. and Hollaender, A. J. Cellular Com/). Physiol. 

 1953, 41 345. 



3 Doherty, D. G. and Burnett, W. T., Jr. Abstr. of Papers, 126lh Natl. Meet. Amer. 

 Chem. Soc. 1954, p, 9C. 



115 



