FREE NITROGEN COMPOUNDS IN PLANTS O81 
non-growing cells, and so to determine the extent to which glutamine could furnish 
nitrogen and/or carbon for protein synthesis. 
The crucial evidence for protein turnover, accentuated in the growing carrot cells, 
was as follows. Under the stimulus of coconut milk a net increase of protein occurred 
but the incorporation of C into certain of the protein amino acids was increased by 
coconut milk several times more than the increase of the total protein, as shown in 
Table V. This led to the idea that far more of these amino acids were entering the 
protein fraction than could be accounted for by the increase in the total bulk of 
protein in the cells. 
This general picture of protein turnover was substantiated by the consideration 
of the specific activity of glutamine in the cells. The essential arguments are re- 
TABLE VI 
TOTAL AMOUNT AND SPECIFIC ACTIVITY OF GLUTAMINE IN CARROT EXPLANTS SUPPLIED 
WITH 14C-LABELED COMPOUNDS 
Data from STEWARD, BIDWELL AND YEMM. 






Slow-growing Fast-growing 
(4C) Compound Time cultures (no C.M.) cultures (+ C.M.) 
Supyied we) Amount Sais tay : vy eine Specific activity 
(ug C) (counts/min|ug C) (ug C) (counts/min| ug C) 
y-AB 22 Bi 285 95 120 
y-AB I 58 182 287 IOI 
y-AB 109 237 118 371 103 
Glutamine 22 47 750 266 583 
Glutamine Or 166 615 563 408 
Glutamine 10g 311 386 g16 348 

capitulated below, and the main data on which they are based are shown in Table VI. 
(1) The fact of protein synthesis is established by the entry of !C from the exoge- 
nous substrate into the protein. 
(2) Free glutamine in the cell had a continuously declining specific activity, and 
especially so when [!4C)glutamine was exogenously supplied. This unexpected fact 
indicated substantial entry of non-radioactive glutamine into the soluble pool (see 
Table VI). Thus, the only evident source for the non-radioactive carbon of the gluta- 
mine which was being formed in the cell must have been protein by breakdown. 
(3) The non-radioactive glutamine being synthesized in the cell did not come 
readily from sugar, because if [!4C|sugar was furnished the glutamine did not become 
radioactive. 
(4) The [#4C}glutamine which was supplied exogenously to the cell could readily 
appear as COg. 
(5) Furthermore, the formation of non-radioactive glutamine with time was much 
more rapid in the rapidly growing than in the slower growing cells. This was shown 
by the decline in its specific activity concurrently with the rapid increase in total 
quantity. 
References p. 692/693 
