100 



E. L. POWERS 



exposed to oxygen. When the irradiated spores are exposed to nitric 

 oxide, abnost complete obHteration of the radical signal is observed 

 (Fig. 5). At first glance this seems to be anomalous, for the biological 

 consequence of heat and the nitric oxide treatment is the same, whereas 

 the physical result appears to be different. However, instead of indi- 

 cating limited usefulness of the experimental approach, the result 

 might be amenable to an interesting explanation. 



Either of two possibilities exist. First, the compound formed by the 

 reaction of oxygen and the radicals remaining after heat annealment 



H 



(e) 



100 gauss 



Fig, 5. — The effect of various treatments on the E8R signal seen in irradiated bacterial 

 spores, (a) The fully developed doublet-triiDlet signal, (b) The signal observed after 

 exposure of the irradiated spores to oxygen. The dotted line is the signal intei'mediate 

 Ijetweea (a) and the heavy line of (b). (c) The effect on (a) of heating the spores at 80"C 

 for 15 minutes, (d) The effect of exposing the heated spores of (c) to oxygen, (e) The 

 signal observed after tlie spores of (a) are exposed to NO. (From Ehret et al., 1960). 



may not be important in the damage that we see, for in the NO-treated 

 cells these cannot be formed, yet the biological result is the same in the 

 two instances. Or, second, reaction of nitric oxide with these radicals 

 brings about cellular damage — that is. the reaction between nitric 

 oxide and the residual, non-annealable radicals is equivalent to the 

 reaction l)etween these residual radicals and oxygen. The reason there 

 is no evidence of the nitric oxide-radical complexes is that after reaction 

 there are no unpaired electrons, but the chemical or biochemical con- 

 sequences are the same as those seen following reaction with oxygen, 

 forming compounds with un])aired electrons that can be measured by 

 the ESR spectrometer. If this is true, we can subdivide the long-lived 



