BIOSYNTHESIS OF PROTEIN 639 

fo} Pool“c Aspartic 
60 x Pool “C Aspartic Exogenous 
12 
C Threonine 
APoo!“C Glutamic 
+Pool “C Glutamic Exogenous 
4G Arginine 





iN 
fe} 
nN 
(e) 

=a 
Oo 




o 



a 

Radioactivity in counts per second()(*)(@)(@ 
nN 






10 
20 40 60 80 100 
Time in minutes 
Fig. 4. Loss of (1#Cjglutamic and [Cjaspartic acid carbon from the cold TCA-soluble fraction. 
Data obtained from cells (approx. 1.0 mg wet wt./ml medium at ¢ = o) briefly immersed in 
medium containing either [4Cjglutamic or aspartic acid and transferred after washing to non- 
radioactive medium containing amino acid supplements (1.0 mg/ml medium) or to non-radio- 
active medium without amino acid supplements. ©, pool [“@Cjaspartic; x, pool {C]aspartic 
plus exogenous [!?C|threonine; A, pool {@C]glutamic; +, pool [C]glutamic plus exogenous 
[72C]arginine. 

OF 
ts 
Oo; | Total 
U0 
c3 So 
o 
4 eas 
c KO Neate Precipitable Fraction 
Qa 
22 Yh 
= 
=| 
} 
U 
c 
2; 
= 14 
= 
Fa old TCA Soluble Fraction 
0 
° 
no) 
o 
or 


(2) 
100 120 140 160 180 200 220 
Minutes 
O 20 40 60 80 
Fig. 5. Time course of incorporation of [Cjglutamic acid. Initial exogenous concentration was 
0.002 mg glutamic acid/ml medium. 
DISCUSSION 
Endogenously formed amino acids 
At some point in the synthesis from fructose the family heads (glutamic, aspartic 
and pyruvic acids) are formed and become available to the internal pool where 
References p. 645 
