UPTAKE OF TYROSINE BY BRAIN Sap! 
TABLE VII 
EFFECT OF OTHER AMINO ACIDS ON THE UPTAKE 
OF L-TYROSINE BY BRAIN SLICES 
Slices incubated for 60 min in buffer containing L-tyrosine 
(rt x ro-* M) and the indicated amino acids (1 xX 10°? M). 


Intracellular concn. (ug/ml) 
Compound sits pie eee 
Medium concn. (g/ml) 


Control 2.60 
L-Glutamate 2.51 
y-Aminobutyric acid 3.04 
L-Arginine 2.55 
L-Histidine Te 77; 
L-Tryptophane 1.28 
L-Phenylalanine T.15 
L-Valine Med iS 
p-Fluoro-pi-phenylalanine 0.90 

Also those which were not effective 77 vivo were not effective 77 vitro. The inhibitors, 
however, acted only on the concentrative component of uptake by the slice and did 
not affect the diffusion uptake. 
When the structural and steric specificity of the slice uptake were studied (Fig. 5) 

2.00 
180F 
o4 





O—— |-TYROSINE 
@——e [)-TYROSINE 
4——-4 | -Q-METHYLTYROSINE 4 
O——) TYRAMINE 
m8 P-HYDROXYPHENYLACETIC ACID 


TISSUE CONCENTRATION (1g /gm ) 

0 20 40 60 80 100 {20 140 
MINUTES 
Fig. 5. Uptake of tyrosine and related compounds by brain slices. 
it could be seen that the molecules taken up by brain im vivo were concentrated by 
brain slices (L-tyrosine, tyramine, a-methyl-1-tyrosine). On the other hand, D-tyrosine, 
which was taken up to a very small extent im vivo, was taken up as well as L-tyrosine 
in vitro. In addition, p-hydroxyphenylacetic acid, which did not enter the brain 7 
vivo, did enter the slice, probably passively. The factors which modified the uptake 
of tyrosine by the slice had no effect on the uptake of p-hydroxyphenylacetic acid 
(Table VIII) indicating that they affect only the concentrating mechanism. 
References p. 553 
