408 S. GARD AND O. MAAL0E 



could be completely inactivated by nitrite without viscosity changes or any 

 other signs of denaturation; they concluded that inactivation could be 

 accounted for entirely by deamination. According to these authors, removal 

 of one single amino group was sufficient to render the nucleic acid molecule 

 completely inactive. 



Many of the reactions dealt with in this section are strongly affected by 

 catalyzers. Of particular importance are certain metal ions, primarily Fe 

 and Cu. Free radicals presumably appear by oxidation of ferrous ions which 

 would explain the pronounced catalytic effect of this ion. In studies of virus 

 inactivation very little attention has been paid to these facts; consequently, 

 the scattered observations on the effects of oxygen, hydrogen peroxide, 

 ascorbic acid, etc., are difficult to evaluate. 



According to Sizer (1945), oxidation reduction stability curves are equally 

 specific and characteristic for individual enzymes, as are pH stability curves. 

 Some enzymes are stable over an extended E;; range; at potentials beyond 

 the stabihty range increasingly rapid inactivation takes place. Others show 

 a stability ojDtimum, the rate of inactivation gradually increasing with shifts 

 in potentials in either direction. Similar systematic studies on viruses have 

 not been carried out. It is generally assumed, however, that reducing sub- 

 stances like cysteine have a preservative effect (Zinsser and Tang, 1929; 

 Zmsser and Seastone, 1930; Long and Olitsky, 1930; Perdrau, 1931; Amos, 

 1953). 



2. Oxygen 



Oxidation through aeration is supposed to be one of the contributing 

 factors in "spontaneous" inactivation of viruses. The underlying evidence is 

 mainly indirect. Viruses are known to be sensitive to other, more potent 

 oxidants; the preservative effect of lyophilization or addition of reducing sub- 

 stances points in the same direction; a few direct experiments on the effect 

 of increased oxygen pressure were also carried out (Perdrau, 1931). The rela- 

 tive importance of aeration in this respect was never fully established, 

 however. As already pointed out, inactivation of viruses must always be 

 considered a complex phenomenon, the resultant of several simultaneous pro- 

 cesses. In the so-called spontaneous inactivation in aqueous media at least 

 four different factors are to be taken into consideration: H+ and 0H~ ions, 

 heat, and oxidation reduction potential. Within the "stability" range, where 

 pH changes have little effect upon the rate of inactivation, the direct action 

 of H+ or 0H~ must obviously be negligible, the rate-determining factor being 

 either oxidation or heat denaturation. These two reactions should be ex- 

 pected to differ considerably with regard to the energy of activation. As 

 already pointed out, Arrhenius plots of "thermo"-inactivation have yielded 

 values varying from less than 30,000 to 195,000 cal./mole; not infrequently, 



