DYNAMIC ASPECTS — PERMEABILITY AND TRANSPORT 595 
THE MECHANISM OF AMINO ACID POOL FORMATION 
IN 2 SCHERT CHITA COE 
R. J. BRITTEN anp F. T. McCLURE* 
Carnegie Institution of Washington, Department of Terrestrial Magnetism, 
Washington, D.C. and Johns Hopkins Applied Physics Laboratory, Silver Spring, 
Md. (U.S.A.) 
SUMMARY OF EXPERIMENTAL RESULTS 
Bacteria maintain internally synthesized small molecules at high internal concen- 
trations and in addition have the capacity to concentrate many compounds from 
the environment. Since the majority of these compounds are intermediates in syn- 
thesis they are collectively termed the pool of metabolic intermediates, or, simply, 
} 

oO 
an 
Relative specific 
radioactivity 
fo} 





rst component of pool 

5, 
5 
TT 


Pool size (moles/| cells) 
\& Initial total rate of incorporation 
+ 


*~ Rate of internal synthesis 

Rates (moles/I cells/sec) 
3 


| 
| 
Ser iil ares Arte bo TA 
7? 6 -5 -4 3 
B fo) fo} 10 10 10 
External concentration (moles/I) 

Fig. 1. Proline pool formation in E. coli at 25° (log log plot). The experimental points are derived 
from a set of eight simultaneous measurements of the time course of incorporation of radio- 
active proline, except the point at 4.2 x to 4 M which is the average of several measurements 
of the saturation pool size. &, ratio of specific radioactivity of the pool (at the time it reached 
its maximum value) to that of the added radioactive proline. @, maximum pool size reached 
versus concentration present at that time. ——-—, prediction of the carrier model for the size of 
the major component of the pool alone. +, initial total rate of incorporation of external proline. 
O, calculated average rate of internal synthesis of proline during the time required for the pool 
to reach its maximum value. (By courtesy of the editor of Biophys. J.) 
the “pool”. However, the state of organization and ultimate chemical fate of exoge- 
nous compounds concentrated by the cell may be different from that of identical 
compounds synthesized by the cell. 
Since the mechanism by which high internal concentrations are maintained is not 
understood and the processes are obviously complex, it appears fruitless to enter 
* Research Associate of the Carnegie Institution of Washington. 
References p. 609 
