AMINO ACID POOL FORMATION IN Escherichia coli 601 
Item 12 shows clearly that the pool has more than one component. This argument 
has been given in detail in the experimental section on exchange. The evidence 
summarized in items 6, 8 and 18 also strongly supports this conclusion. From the 
point of view of the permease model, one might say that the cell has several pool- 
containing compartments separated by osmotic barriers, each containing an appro- 
priate permease, but this is not a pleasant prospect. It seems much more likely that 
at least part of the pool is not in free solution within the cell, as will be discussed 
below. 
TABLE I 
RELATIONSHIP OF PROPERTIES OF THE POOL TO THE MODELS 






Score 
Obseruaisan Permease Carrier 
model model 
Formation and Maintenance 
1. Glucose required for formation + * a 
2. Glucose not required for maintenance — =F 
3. Pools formed slowly at o° = == 
4. Pools maintained at 0° = =e 
5. Pool maintained at 25° in absence of either the amino acid or 
glucose es ai 
6. Pool size versus concentration not Michaelis = ate 
7. Initial rate of formation not proportional to pool size = a 
8. Small pools not generally influenced by other AA but large pools 
are suppressed = Ar 
g. Evidence for catalytic site in general =F =e 
10. Pools may be very large Sly = 
Exchange 
11. Exchange occurs in addition to steady flow through the pool ar an 
12. Rapid exchange occurs in absence of glucose or at 0° = =i 
13. Fast and slow components in exchange at 0° = =i 
14. The 0° exchange rate saturates at low external concentration — i= 
15. The o° exchange rate increases with pool size = Ste 
Osmotic Behavior 
16. Pools removed by sudden reduction in osmotic strength + (ee 
17. Pools immediately re-formed after removal by shock Sn 
18. Different pools removed to different extent by shock -- (3) ** 
19. Maximum pool size increases with osmotic strength of medium — = 
* 4 indicates that the model satisfactorily explains the observation. —, indicates that 
there is a contradiction or that a modification may be required by the experimental evidence. 
** Assuming that the sites may be osmotically sensitive. 
The observation (item 6) that the pool size, far below saturation, does not rise in 
proportion to the concentration could be taken to indicate that there is more than 
one component in the pool or that there are permeases with a variety of affinities 
for a given compound. For a number of reasons this item cannot be considered a 
crucial argument against the permease concept. However, since the permease model 
we are discussing does not predict such a result, it is given a minus score for item 6. 
References p. 609 
