BACTERIOPHAGE INACTIVATION UNDER VARYING CONDITIONS OF IRRADIATION 



It will probably have been noticed that there is an apparent paradox in 

 the relationship between bacteriophage and hydrogen peroxide : I have 

 described it as an inactivating agent for phage, and yet have shown that its 

 formation acts as a protective mechanism. The paradox is resolved if the 

 time factor is taken into account ; the formation of hydrogen peroxide pro- 

 tects the phage only when radiation is delivered within a fairly short time, 

 and the phage sampled immediately afterwards. At low dose rates the 

 hydrogen peroxide can attack the phage during irradiation, the more so 

 since part-inactivated phage particles are counted as survivors in short-term 

 experiments, but may, with longer time lapses, be inactivated by the peroxide. 

 There is evidence that phage is attacked by hydrogen peroxide only when it 

 decomposes, and then only when it decomposes via reducing radicals. In 

 fact it seems justifiable to postulate that any radicals which are removed at 

 the time of radiation by HgOa formation may act as inactivating agents 

 when the HgOg decomposes. The HgOg therefore acts as a bank for radicals, 

 in any experiment in which dose rates are low, or which is of such a nature 

 that a time lapse occurs between the end of irradiation and the measurement. 

 One can take this argument a step further. In biological experiments in 

 which the end product of radical action is not defined in chemical terms, it is 

 often assumed that enhancement of radiation effects implies an oxidative 

 mechanism. But the presence of oxygen allows of the formation of hydrogen 

 peroxide, and therefore, in effect, of the storage of free radicals which would 

 otherwise be lost by recombination into water or into Hg and O^ molecules. 

 The H2O2 may decompose, either under the action of the radiation, or after 

 irradiation ceases, and so give the radicals a further probability of reacting 

 with sensitive systems. If the nature of a radiation experiment is such that 

 dose rates are low, or long term effects are involved, it seems possible that an 

 important role of oxygen may be to make radicals available for later reaction, 

 rather than exclusively to enhance oxidative reactions. 



SUMMARY 



From high dose rate irradiations of bacteriophage under various gas treat- 

 ments, and at various hydrogen ion concentrations, it has been concluded 

 that phage is inactivated by H radicals, in deoxygenated suspensions, and 

 by Og" radical ions, in oxygenated suspensions. In the former, protection 

 may arise in acid suspensions from the reaction H + H+ :i^ Hg"^. The 

 formation of hydrogen peroxide acts as a protective mechanism for the phage, 

 when irradiations are completed in a short time, but the HgOa may later 

 inactivate the phage by decomposing into the radicals which entered into 

 its formation. It is suggested that the presence of oxygen may enhance 

 radiation effects not exclusively through enhancement of oxidative reactions, 

 but also because the oxygen acts as a means for 'storing' radicals which 

 may later become available for reaction with sensitive systems. 



REFERENCES 



1 Anderson, T. F., Rappaport, C. and Muscatine, N. A. ' Le Bacteriophage,' 

 Ann. Inst. Pasteur, 1953, 84 No. 1, 5. 



2 Hershey, a. D. and Chase, M. J. Gen. Physiol. 1952, 36 39. 



3 Garen, a. and Puck, T. J. exp. Med. 1951, 94 177. 



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