AMINO ACID POOL FORMATION IN Escherichia colt 597 
At the present time unequivocal answers do not exist for any of these three ques- 
tions. However, the large body of experimental evidence does provide a restrictive 
set of conditions which theoretical models must satisfy, and supplies a background 
for the formulation of more refined questions. 
The following discussion of the mechanism of pool formation has been abstracted 
from a monograph” and corresponds to the central part of the paper presented at the 
conference. Unfortunately, due to limitations of space, it is impossible to present 
here the experimental observations supporting the 19 items listed in Table I. As a 
compromise five figures are included, having self-explanatory captions. 
100 
080 
-060 
«040 
«020 
010 
-008 
006 
Exchange rate (moles/g wet wt./min) 
004 
002 

0.4 0.6 0.8 1.0 2.0 4.0 6.0 8.0 10.0 20.0 
Pool size (umoles /g wet cells) 
Fig. 4. Rate of exchange as a function of pool size (log log plot). The points were obtained from 
experiments such as that shown in Fig. 3 by fitting the time course of exchange to curves derived 
from the sum of two exponential decays. The numbers beside each point are the external con- 
centrations during exchange in smoles/l. The straight line shown would result if the exchange 
rate were proportional to pool size. (By courtesy of the editor of Biophys. J.) 
The experiments summarized in the figures were performed with Escherichia coli 
strain B (ATCC 11303) (except that of Fig. 5) using the membrane-filter technique 
previously described!. 
It must be pointed out that all of the curves in Fig. 1 except the uppermost one 
are theoretical predictions from the carrier model. These calculations are described 
in the mathematical appendix of ref. 12. 
A partial description of the experimental results has also appeared!: 2: 3; 4; 9. The 
following summary of the principal features of the pool may also be useful: 
1) Passage through the pool appears to be an obligate step for incorporation of an 
exogenous amino acid into protein. 
2) Amino acids present in the pool are incorporated into protein at random, 
regardless of the length of time they have been in the pool. 
References p. 609 
