STUDIES ON THE INCORPORATION OF ARGININE 



301 



same preparation of acceptor RNA was used. The initial reaction volume 

 was I -5 ml., and included 100 fx\. of Fraction I. Aliquots of 0-5 ml. were 

 removed at different times and assayed as described under Methods. The 

 results are shown in Fig. i where the formation of arginine-RNA is rep- 

 resented by circles (open for Fraction I^ and filled for Fraction Ij) and 

 the formation of leucine-RNA is denoted by triangles (open for Fraction 1^ 

 and filled for Fraction I^). The figure includes an experiment with a 

 twenty-times diluted sample of Fraction I^ (open squares) to show that 

 this reaction like that with leucine procedes linearly with time. As Fig. i 



II 



30 



f1 

 I I 



Time in minufes 



Fig. I. Rate of formation of arginine-RNA (filled and unfilled circles) and 

 leucine-RNA (filled and unfilled triangles). The enzyme sources were Fraction I^^ 

 obtained from cells grown in the presence of arginine (open circles and triangles), 

 and Fraction I^ from cells grown in the presence of leucine (filled circles and 

 triangles). The open squares represent the formation of arginine-RNA with a 

 twenty-times diluted sample of Fraction I.^. 



shows, the addition of either amino acid to the growth medium is without 

 effect on the formation of either activating enzyme. 



EFFECT OF GUANIDINO DERIVATIVES ON THE ARGININE-ACTIV.'VTING ENZYME 



Certain guanidino derivatives were tested for their effect on the rate 

 of formation of arginine-RNA. Purified arginine-activating enzyme (about 

 3 /xg. per assay) was used in all experiments with arginine, and Fraction I 

 was used in the experiments with the amino acid mixture (the alga protein 

 hydrolysate). Table I shows that canavanine and streptomycin were found 

 to be inhibitory whereas nitroarginine was slightly stimulatory and sul- 

 phaguanidine without a definite effect. 



