GENERAL DISCUSSION 347 



biochemical amplification of the radiation effect. In view of these secon- 

 dary but very rapidly advancing changes, the physico-chemical proper- 

 ties of elementary structures are altered much more significantly as 

 emerges in the variation of the iso-electric point of the nucleoproteins 

 (Shal)adasli) and in the correlation of the free and bound lipids (Doemin), 

 and leads to a more significant change in the co-ordinated work of the 

 enzymes, to an amplification of the activity of some and the weakening 

 of others. The amplification of the enzymatic oxidation reactions, 

 especially in the presence of oxj^gen, leads to an anomalous concentra- 

 tion of some active compounds (e.g. peroxides of unsaturated acids 

 — Chevallier and Bacq — of active quinones, of semiquinones which 

 easily give active free radicals — Kuzin) which complete destruction of 

 the sub-cellular structures, inhibit and distort mitoses (Kuzin), convert 

 the initial concealed injuries, for example in chromosomes, to manifest 

 breaks (Hollaender, Shapiro). When the intensity of the processes 

 described is adequate destruction of the metabolism of the cell proves 

 to be so considerable that it will lead to lysis, to the death of the 

 cell. This increment in the destruction of the individual exchange 

 reactions, will in such a case be of an avalanche nature, and will be 

 formally described by those equations which are applicable to chain 

 reactions in purely chemical systems. All the conditions which delay 

 the unfolding of this metabolic chain will delay the transition of the 

 concealed damage to open damage, amplify the probability of the 

 return of the initially destroyed structures to the initial state, and by 

 this very fact assist the conservation of the cell. This probably accounts 

 for the mechanism of action of many protective substances. (Bacq 

 and Alexander, Shapiro, Hollaender, Grayevsky). 



ZEITLIN : In DNA solutions under the influence of various factors (the 

 binding of proteins or amines to the DNA etc.) there is observed in 

 many cases a reversible two-fold drop in the characteristic viscosity 

 without a variation in the molecular weight. Therefore, this variation 

 in viscosity may be treated as a consequence of a change in the con- 

 figuration of the DNA molecule, possibly connected with a reduction 

 in the degree of symmetry which someM^iat tentatively we shall call 

 "compression". 



We have studied jointly with Spitkovsky and Tongur the radiosensi- 

 tivity, for moderate radiation doses, of native DNA and also of DNA in 

 which compression has occurred. We have studied the behaviour of DNA 

 in dilute solutions in which intermolecular interactions can be excluded. 



DNA in a compressed condition proves to be much more radio- 

 resistant than ordinary DNA. For doses of 5 kr, the fall in the viscosity 



