THE BIOCHEMICAL MECHANISM OF THE 

 DISTURBANCE OF CELL DIVISION BY RADIATION 



A. M. KUZIN 



Institute of Biophysics, U.S.S.R. Acadeuuj of Science, Moscow, (J.S.S.Ii. 



SUMMARY 



X -irradiation of fully grown leaves of Vicia faba, causes almost immediate 

 activation of oxidative enzymes of the polyi^henoloxidase and pei-oxidase type. 

 The products of oxidation of tyrosine (or similar substances) increase. These 

 block DNA sjoathesis and thus prevent cells entering mitosis. 



The appearance of "antimitotics" was demonstrated both by post-irradiation 

 observation of the remote inliibition of mitosis in the points of growth (which 

 were screened during the irradiation) and also by extraction of the "antimitotics" 

 from the irradiated leaves, their purification and testing on un-irradiated roots 

 of Vicia faba. 



It was shown by model experiments, that low molecular weight products of 

 the enzymatic oxidation of tyrosine possess antimitotic activity, i.e. the capacity 

 to combine with highly-polymerized DNA and to protect DNA in vitro against 

 radiation-induced depolymerization. 



There has been much radiobiological literature devoted to the 

 specially imiwrtant problems of the direct action of radiation on the 

 DNA of the cell nucleus and its indirect influence on the inhibition of 

 cell division through altered metabolic processes in the cytoplasm. 



An analysis of this problem was given by Gray (1956) at a radio- 

 biology symposium. Facts and considerations presented by him and by 

 Alexander, together with later results, lead us to draw the conclusion 

 that processes going on in the cytoplasm of irradiated cells play a great 

 part in the inhibition of cell division by radiation. 



Shabadash's (1960) investigations carried out in our laboratory, 

 showed considerable shifts of the ribonucleoproteins of cell mitochon- 

 dria (the isoelectric point) within one minute of the animals being 

 exposed to radiation at a dose of 1,000 roentgens. This phenomenon un- 

 doubtedly leads to an alteration of the oxidative processes regulated 

 by these cytoplasm structures. 



On the other hand Strajevskaya and Struchkov, while endeavouring 

 to reveal physico-chemical changes in DNA isolated immediately after 

 the animals had been irradiated, found that this substance was rather 

 stable when the influence of cytoplasmic DNase, activated by the radi- 

 ation, was completely eliminated. The results of measurements of the 



223 



