230 A. M. KUZIN 



Table V. Peroxidase activity in maize root and leaves. 



These observations gave us the idea that products of enzymatic 

 oxidation of phenols and jiossibly first of all. tyrosine, are substances 

 which slow down cell division after irradiation. This suggestion was in 

 a good agreement with the following experimental facts: 



1. After the removal of proteins, which coagulate on heating, extracts 

 of irradiated leaves preserved their antimitotic activity. 



2. After dialysis of protein-free filtrates antimitotic activity was 

 observed in the fraction that diffused through the collodion mem- 

 brane. This is evidence for the low molecular weight of the anti- 

 mitotics investigated. 



3. When protein-free filtrates were chromatographed on alumina the 

 antimitotics were absorl)ed completely. The filtrates were quite in- 

 active. Many diphenols, semi-quinones and quinones are strongly 

 absorbed to alumina. 



4. By fractional elution of the absorbed substances with a weakly 

 alkaline solution we succeeded in obtaining a fraction from extracts 

 of irradiated leaves that showed antimitotic activity from extracts 

 of control leaves, almost without activity. 



5. The ultraviolet absorption spectrum showed a distinct maximum at 

 280 m/n, in the fraction from irradiated leaves as may be seen from 

 the curves given in Fig. 6. 



The determination of polyphenols by means of their reaction ^\'itli 

 the iron tartrate reagent showed an increase in quantity in extracts 

 from irradiated leaves. If the content of the quinonoid products of 

 oxidation of tyrosine actually increase, then they should behave as 

 strong oxidizing agents like peroxides. The experimental data are given 

 in Table VI. 



Our conclusion about the important role of quinonoid products of 

 the enzymatic oxidation of tyrosine in inhibiting mitosis under the in- 

 fluence of ionizing radiation was proved by model experiments. We 

 oxidized dilute solutions of tyrosine in the presence of a purifled pre- 



