306 H. G. BOMAN, I. A. BOMAN 



fraction [17]. There may thus be considerable differences in turnover 

 number between activating enzymes. 



The experiments in Fig. i show a comparison of the incorporation of 

 arginine and leucine when the enzyme fractions had been obtained from 

 cells grown in the presence either of arginine or of leucine. The results 

 show that the addition of the amino acids to the media had no effect on 

 the level of the corresponding activating enzyme and that the repression 

 mechanism found for the enzymes in the biosynthesis of arginine [18] 

 does not operate on the arginine-activating enzyme. Further support for 

 this conclusion is provided by the results of several experiments in which 

 no appreciable difference was found between the quantities of arginine- 

 activating enzyme obtained from the wild type and the arg . R" mutant. 



/;/ vivo experiments have earlier shown that canavanine inhibits growth 

 by interfering with the utilization of arginine in protein synthesis [19]. 

 The present finding of the inhibition of the arginine-activating enzyme 

 suggests this step as the site of action of canavanine. Since the enzyme 

 from the mutant is as sensitive as that from the wild type, the mechanism 

 of the resistance in the mutant does not involve an alteration of this enzyme 

 (cf. ref. 20 and 21). 



The experiments in Table I show that streptomycin inhibits the 

 formation of arginine-RNA and that this inhibition is greater for arginine 

 than for a mixture of all amino acids. Streptomycin is known to complex 

 with nucleic acids [22] and it is difficult to exclude that this presumably 

 non-specific effect contributes to the inhibition we have recorded here, 

 although no precipitation occurred in the presence of the buffer used in 

 our experiments. The increased sensitivity of the arginine incorporation 

 compared to that of the mixture of all amino acids (including arginine), 

 though rather slight, indicates some degree of specificity for the inhibition 

 of the formation of arginine-RNA. Some further support for a relation 

 between the utilization of arginine and the action of streptomycin is 

 suggested by the fact that Gorini [23] has obtained a mutant which 

 requires either arginine or streptomycin. It has also recently been found 

 that the genes for streptomycin resistance, the arginine repressor and some 

 of the arginine synthesizing enzymes are closely linked [6]. 



Davis and his co-workers [24] have recently shown that streptomycin 

 damages the cell membrane but they have concluded that this action though 

 necessary, may not be sufficient to account for the bactericidal effect. It 

 may well be that both the specific action of streptomycin in the incorpora- 

 tion of arginine into acceptor RNA and its non-specific complex formation 

 with nucleic acid contribute to the bactericidal action. 



In vivo experiments with nitroarginine showed that it neither affects 

 growth, nor does it replace arginine for the growth of an arginine-requiring 

 mutant. The i^/^ increase in the rate of formation of arginine-RNA 



