COFACTORS OF EnZYMIC ADAPTATION 



217 



Fig. 2 gives the frequency of mutants as a function of 

 euflavine concentration. It is interesting to find that the 

 relation is not Hnear. The two simplest explanations of this 

 result are either that two or more molecules of euflavine are 

 necessary to produce a mutational event, or that we are 

 dealing here with a threshold phenomenon. This last inter- 

 pretation means that a concentration of euflavine up to 

 3 X lO^'^M is rendered ineffective, or neutralized by the cells. 



Table III 



Competition between euflavine and purines 

 IN induction of mutation 



Expt. G 12. Concentration of adenine and guanine in mg./ml. 



Addition of a mixture of nucleic acid constituents suppresses 

 the mutagenic action of the dye. Their antimutagenic action 

 is competitive and may be complete. By studying the sup- 

 pressive effect of individual nucleic acid bases, either singly 

 or in various combinations, it was found that adenine is by far 

 the most effective; guanine and thymine are about three 

 times less active than adenine. Uracil, cytosine, ribose and 

 deoxyribose are ineffective (Table III). 



