THE ROLE OF H2O0 229 



Ionizing radiations produce also reductions, as shown by the reduction 

 of KMn04, Ce(S04)2, KCIO3, KNO3. Reduction reactions, however, 

 seem to be of no biological importance. In fact, neither oxidized 

 glutathione nor diphosphopyridine nucleotide nor oxidized cytochrome 

 c was reduced on x-ray irradiation. 



The Role of H2O2 



A word may be said about the importance of H2O2 on the mechanism 

 of action of ionizing radiations. That H2O2 is produced on irradiation 

 of oxygenated water is a well-known fact. As Bonet-Maury and Frilley 

 demonstrated (10), the production of H2O2 can be used as a simple 

 method of measurement of x-ray intensity. However, the role of H2O2 

 in the irradiation of living cells has not yet been determined. The 

 amount of H2O2 formed in oxygenated aqueous solutions, such as bio- 

 logical fluids, is always less than that formed on irradiation of distilled 

 water because the electrolytes contained in those fluids diminish H2O2 

 formation; furthermore, the universal distribution of catalase w^ill further 

 diminish the amount of H2O2. Whether the catalase — H2O2 complex 

 will act as an oxidizing agent, as Keilin and Hartree (11) have show^n 

 on the oxidation of ethyl alcohol, is not known. The possible role of 

 H2O2 could be postulated from the experiments of Evans (12) on inhi- 

 bition of the fertilizing power of sea-urchin sperm, and from our own 

 experiments on inhibition of respiration (13) w^hen the sperm is suspended 

 in x-ray-irradiated sea water. However, the x-ray dose rec^uired to 

 produce such effects is much higher than that required to inhibit both 

 functions (fertilization and respiration) on direct irradiation. The in- 

 hibition of respiration produced by x-irradiated water occurred even 

 2 hr after irradiation. Moreover, the inhibition was not produced by 

 changes in the organic matter, or the salts of sea water, for similar 

 inhibition was observed on irradiation of distilled water and addition 

 of salts afterwards (Table -4). It is obvious that H2O2, when added 



TABLE 4 



Inhibition of Sea-Urchin Sperm Respiration by X-Irradiated Water 



(TJie necessary amount of salts to make artificial sea water was added at different 

 times after irradiation. Irradiation: 100,000 r) 



Experimental Inhibition, 



Condition % 



Soon after irradiation 68 



30 min after 65 



60 min after 60 



