696 H. EAGLE AND K. A. PIEZ 
metabolic interconversion between serine and glycine on the one hand, and alanine 
on the other (cf. Table IT). 
The a-amino group of the nutritionally non-essential amino acids derives solely 
from glutamic acid, this despite the fact that, as BARBAN has shown®, cultured 
human cells contain a broad spectrum of transaminases. This further illustrates the 
point that the presence of a given enzymatic activity in a cell extract is no necessary 
indication of its physiological significance. 
In these cultures we have not yet encountered end-product inhibition (“negative 
feedback”) in amino acid biosynthesis. In all examples so far examined, the provision 
of pre-formed nutritionally non-essential amino acid has not inhibited its biosyn- 
thesis?. 
Intracellular amino acids and amino acid transport 
The nutritionally essential amino acids are concentrated by the cell to varying 
degrees’ (cf. Table III). The nutritionally non-essential amino acids, which are 
TABLE IT 
THE AMINO ACID POOL OF THE HELA CELL 
From PIEZ AND EAGLE”. 


(A) (B) (A) (B) 
Concentration Concentration Distribution 
im cell water in medium ratio 
(mM) (mM) 
[" Arginine (0.03) 0.017 2 
Glutamine 8.1 0.72 II 
Histidine 0.20 0.032 8 
Nutritionally | Isoleucine 1.00 0.125 8 
essential | Leucine 0.73 0.097 8 
amino acids, Lysine 0.29 0.119 3 
present in Methionine 0.19 0.035 5 
medium Phenylalanine 0.52 0.069 8 
Threonine 0.96 0.178 5 
Tryptophane <O.1 (0.012) <8 
Tyrosine 0.81 0.087 9 
Valine 0.79 Ona 7 
Alanine 1.43 0.081 18 
Asparagine 0.15 <0.005 > 30 
Nutritionally Aspartic acid 127 0.012 106 
non-essential Cystine 0.05 0.023 2 
amino acids, Glutamic acid 10.80 0.794 14 
synthesized Glutathione 4.42 <O.1 > 44 
by cell Glycine 0.79 0.005 158 
Proline 0.80 <0.005 > 160 
Serine 0.03 0.003 10 
p-Alanine 0.50 <0,002 > 250 
y-Aminobutyric acid 0.17 <0.002 >85 
Related Ammonia 4.90 1.646 3 
compounds Glycerophosphoethanol- 
produced amine 1.36 <0.002 > 680 
by cell Ornithine 0.10 0.046 2 
Phosphoethanolamine 0.02 <0.002 >10 
Taurine 14.30 (0.002) 7150 
Urea (0.55) (0.43) I 
References p. 705 

