596 Ree BRITE NGAN DEE he MCChUiRiE 
into an extended discussion of the meaning of the term “pool”. Therefore, we will 
simply define the “pool” as the total quantity of low molecular weight compounds 
which may be extracted from the cell under conditions such that the macromolecules 
are not degraded into low molecular weight subunits, for example, brief exposure 
to 5% trichloroacetic acid at room temperature. 
aS 
[o) 
[4c] Proline 
limited glucose 
WwW 
Radioactivity in counts/sec 
Dv) 

Time (min) 
Fig. 2. Maintenance and exchange of pool proline in the absence of glucose. In both experiments, 
growing cells were suspended at time zero in medium containing 10 g/ml glucose and 0.87 g/ml 
[#?C]proline. For curve A a small quantity of [“C]proline was added at time zero. For curve B 
an equal quantity of [4C|proline was added at 13 min. In each case the upper curve ( (©) re- 
presents the total [14C|proline taken up, and the lower curve (x ) the “C incorporated into pro- 
tein. The difference is the [Cjproline in the pool. 
Experiments have, 1n general, been designed to answer the following three questions: 
What are the mechanisms by which exogenous compounds are concentrated? What 
states of organization exist for compounds in the pool? What is the relationship of 
the pool to the mechanism of macromolecular synthesis? 

70 
60 
50 F 
| 
30 
T 
Radioactivity of the pool 



lot 1 1 1 
0 | 2 3 
Time (h) 
Fig. 3. Time course of exchange of the proline pool at 0°. The log of the radioactivity of the pool 
is shown as a function of time after {!2C}proline was added (10~4 W) to a suspension containing 
a [14C]proline pool of 2.9 x 10~® moles/g wet wt., in equilibrium with external [!C]proline 
(io) <P rome gator 
References p. 609 
