640 D. B. COWIE 
conversion to their respective family members occurs. During exponential growth 
the production of the “parental” amino acids is sufficient to supply all the material 
required for the internal pool. This pool remains fixed in size and composition. 
Attempts to expand the pool by reducing the rate of protein synthesis by lowering 
the temperature quickly to 14° resulted in an equal reduction in the flow of internal- 
pool carbon. When the temperature was raised concurrent resumption of the syn- 
thesis of protein and pool occurred®. 
This close correlation between the internal pool and protein synthesis becomes 
even more apparent when exogenous supplements are employed to alter the fructose 
carbon flow. 
Expandable pool material 
When exogenous amino acids are present the cell accumulates these amino acids 
to Jevels exceeding their external concentrations. This system resembles the amino 
acid permeases found in Escherichia coli7. The amino acids accumulated are con- 
tained in a concentrating or “expandable” poolt; > and have significant differences in 
AUN SILAS, WY 
STEADY-STATE DISTRIBUTION OF RADIOCARBON AMONG POOL 
AND PROTEIN AMINO ACIDS* 


Pool quantity Protein quantity 
Component of compound of compound 
(umoles|g dry wt.) (umoles|g dry wt.) 
Isoleucine—leucine TL 7 785 
Lysine 2 625 
Glutamic acid 290 640 
Aspartic acid 9 762 
Valine 05 512 
Alanine 240 695 
Threonine 8 455 
Serine 8 600 
Proline 7 287 
Arginine 63 210 
Glycine 108 488 
°% accounted for 87 85 

* Data obtained from cells growing exponentially for many gener 
ations in C medium containing [4C)fructose. 
their characteristics which permit their easy distinction from the internal pool 
amino acids. 
1. The degree of accumulation is dependent upon the kind of exogenous amino 
acid supplied, their external concentration and the presence of other exogenous 
material. Its size and composition are therefore highly variable. 
2. No amino acid interconversions take place in this pool. When radioactive 
threonine was made available (50 wmoles/ml medium; Table III, line 1) 90% of 
References p. 645 
