DYNAMICS OF AMINO ACIDS IN PLANTS 661 
time of the experiment. Glycine presented an anomaly, saturating only slowly, 
although present in large quantities in protein. In this case, as in the glutamic acid, 
it was recognized that dilutions from other reactions and/or other pools, may com- 
plicate the kinetics. Indeed, one of the major conclusions by these investigators is 
that the isotopically active pools constitute less than half the total pools, and that 
there may be two or more pools per amino acid. 
60 
@ ALANINE 
4 GLUTAMIC ACID 
SPECIFIC ACTIVITY FOLLOWING 
2MIN EXPOSURE TO '*COp 
counts/min/jg AMINO ACID 

FEEDING TIME 
08 Fig. 2. Time changes of alanine and glu- 
tamic acid activity in tobacco leaf pun- 
tiMIN AFTER FEEDING) ches exposed to 14CO, for 2 min. 
An experiment indicative of the complexity of interpretation involved the feeding 
of 1 mg of [2-!@C]glycine to an excised tobacco leaf. Analysis of the major fraction 
of the leaf showed the distribution summarized in Table IV. The extensive con- 
version of glycine to starch in this excised leaf may reflect the general pathway 
of protein degradation in excised leaves. The surprising variability of this metabolism 
is illustrated in the wide distribution of the initial glycine activity into the other 
amino acids of protein simultaneously synthesized in the excised leaf (Table V). 
Effects of light and age 
Certain other observations made at about this time appear to bear repeating, for 
example, the effect of light and of age. The feeding of CO, for a 20-h period to a 
soybean leaflet in the dark, resulted in the distribution shown in Table VI 
in which it is seen that there is a remarkable incorporation of #C into polymeric 
substances. The ethanol-soluble fraction, however, was by far the most prominent, 
and of these compounds, the most prominent is arginine, which accounts for 35°% 
References p. 666 
