662 S. ARONOFF 
TABLE IV 
DISTRIBUTION OF ACTIVITY IN EXCISED TOBACCO LEAF FED 
[2-4C]GLYCINE 
From RACUSEN AND ARONOFF, unpublished results. 

Activity 
Leay frachon (counts/min) 

80% aq. ethanol extract 248 000 
80% aq. ethanol residue 400 000 
a) crude fiber 19 800 
b) starch 280 000 
c) protein 120 000 


of the free aminoacid fraction, although none is found in the protein (Table VII). The ma- 
jor portion of the radioactivity (75°) is in the guanido-carbon, and consequently 
parallels, in part, the distribution found in the Cyanophyceae (e.g. Synechococcus and 
Nostoc) where citrulline is generally a major product of CO, fixation! both in the 
light and in the dark. The small amount of photosynthetic arginine found as free 
’ 
DABEE Vi 
DISTRIBUTION OF ACTIVITY IN AMINO ACIDS OF TOBACCO LEAF PROTEIN 
FOLLOWING UPTAKE OF [2-!C]GLYCINE IN THE LIGHT 
From RACUSEN AND ARONOFF, unpublished results. 

Amino acid “o pene Amino acid a pees 
Asp 9.4 Ala Tne 7, 
Glu 10.3 Phe A 
Ser 26.2 Leu 5.6 
Gly 22.5 Others* 9.4 

* Roughly equally distributed between tyr, val, pro, arg and cys (cystine not identified 
positively). 
amino acid in soybean leaves is not far from that resulting in the dark with an 
equivalent amount of CO, and equal time. The relatively small amount is therefore 
interpreted not as an inhibition, but simply as not being accelerated by photosyn- 
thesis, as are others. On the other hand, the extremely low values (~ 1%) of free 
glycine and alanine, compared to corresponding values in the light (12.7 and 5.4%, 
respectively) suggest that in the light these amino acids are being made more rapidly 
than they can be incorporated into protein. 
The experiments described above were all conducted with mature, that is, non- 
expanding leaves, in an effort to separate problems of turnover from those of accre- 
tion. The amino acids from “CO, fed to young leaves differed from the mature in 
two major respects, both related to the so-called “indispensible” amino acids. First, 
References p. 666 
