660 S. ARONOFF 
considerations of the ratio of matter input to pool size must also be considered, 
especially when their values approach within a single magnitude of each other. 
Thus, it might be expected that alanine, which is known from short-time experi- 
ments to be in virtual equilibrium with the photosynthetic cycle, would have isotopic 
kinetics of the simplest type: a single input and output, where the log specific activity 
versus t should be linear. As Fig. 2 shows, this is certainly not the case. Furthermore, 
EAB EE VOL 
DISTRIBUTION OF RADIOACTIVITY IN FREE AMINO 
ACIDS OF TOBACCO AND SOYBEAN LEAVES 
AFTER I H PHOTOSYNTHESIS IN CO, 
From RACUSEN AND ARONOFF, unpublished results. 


Amino acid Soybean Tobacco 
Asp 17.4 14.2 
Asp-NH, ibiiait 14.7 
Glu 14.3 | 
Giu-NH, 1.0 f aie 
Gly 2G 6.4 
Ser 44.5 25-5 
Ala 8.0 7.9 

how does one interpret the case of glycine, or aspartic acid, which virtually does 
not change over the entire period, or of serine, which appears to have an initial metab- 
olism, followed by a fall to a relatively constant value? The simplest interpretation 
of the latter data is to presume the existence of isolated pools, e.g. the vacuoles, 
TABLE III 
SPECIFIC ACTIVITY OF FREE AMINO ACIDS OF TOBACCO LEAF PUNCHES 
AS A FUNCTION OF TIME FOLLOWING 2 MIN PHOTOSYNTHESIS IN 4CO, 
From RACUSEN AND ARONOFF, unpublished results. 


Amino acid 5 min I5 min 30 min 60 min 
Asp 72.0 85.4 75.0 69.2 
Asp-NH, 0.0 22.6 23.6 71.5 
Glu g.2 71.0 100 152 
Gly 37.4 Bie 2A Bite 
Ser 3360 219 120 124 
Ala 700 214 59-5 38.2 

which do not metabolize and turn over very slowly; but this is not the sole inter- 
pretation. 
It is interesting to compare these data with those obtained by SMITH e¢ al.> where 
4CO, was fed continuously to a steady-state system of photosynthesizing Chlorella. 
Here, too, saturation was shown to be quite early for alanine and aspartic acid; but 
saturation was never attained for glutamic acid and glutamine in the half-generation 
References p. 666 
