BASIC RADIATION BIOCHEMISTRY 



263 



Lea (1946) has developed theoretical formulas for this protection taking 

 into account the collision frequency of radicals in relation to the molecular 

 size of solute molecules. Dale, Da vies, and Meredith (1949) have mod- 

 ified these formulas, since their results show that in certain cases the pro- 

 tective power per unit mass of protector (Q) decreases with increasing 

 amounts of protector (see Fig. 4-4), whereas the simple concept of sharing 



O 3 



(0 



10^ 



10^ 



10" 



10^ 



CONCENTRATION, /ig/ml 



-«- -o- DIMETHYLUREA, WITH C.P., 30 ;ig/ml 



° = GLUCOSE, WITH C.P., 30;ig/ml 



^ ^ GLUCOSE, WITH C.P., 90 /ig/ml 



Fig. 4-4. Relation between protective power, Q, and concentration of protector with 

 carboxypeptidase (C.P.) as the indicator. Curves are theoretical and points experi- 

 mental. (Dale, Davies, and Meredith, 1949. Reproduced by permission of the editors 

 of the British Journal of Cancer.) 



of radicals predicts a constant value for Q. The new formulas assume 

 that a protector molecule is able to hand on energy to an indicator mol- 

 ecule. This may be in the form of energy of excitation. Alternatively, 



Table 4-2. Protective Power per ^Molecule Q of Various Protectors with 



Carboxypeptidase (C.P.) and Alloxazinadeninedinucleotide (D) as Indicators 



(Reproduced by permission of the editors of the British Journal of Cancer.) 



