550 G. GUROFF AND S. UDENFRIEND 
TABLE V 
EFFECT OF AEROBIC SUBSTRATES ON L-TYROSINE UPTAKE 
BY BRAIN SLICES 
Figures in parentheses indicate number of incubations. Slices 
incubated for 60 min in 10 ml of Krebs—Ringer—bicarbonate 
buffer containing L-tyrosine (1 x 1to-* MW) and the indicated 
substrate (I x Io 2 M). 

Intracellular concn. (ug/ml) 




Compound ——. 
Medium concn. (ug/ml) 
Control 2.73 + 0.28* (36) 
Succinate 2.55 (4) 
Citrate 2.13 + 0.13 (4) 
Acetate 2.53 (6) 
a-Ketoglutarate 3.05 (6) 
Pyruvate 3.51 + 0.40 (14) 
Fumarate Dae (2)) 
Isocitrate 2.38 (2) 
Oxaloacetate 2.49 (2) 
Malate 2.51 (2) 

* Mean + standard deviation. 
was markedly stimulated. Pyruvate also enhanced uptake (Table V) but aerobic 
substrates were completely ineffective. In this regard it could be shown (Table VI) 
that dinitrophenol, iodoacetate, cyanide, and azide were effective inhibitors of the 
concentrative portion of the uptake. Raising the Ca?+ concentration of the buffer 
increased the tyrosine uptake whereas increases in the K+ concentration decreased it?. 
The inhibition of tyrosine uptake by other amino acids was investigated in vitro 
(Table VIT) and it was observed that the same classes of amino acids were effective 
inhibitors of uptake by the slice as were inhibitors of uptake by the intact brain. 
TABLE VI 
EFFECT OF METABOLIC INHIBITORS ON THE UPTAKE 
OF L-TYROSINE BY BRAIN SLICES 
Slices incubated for 60 min in to ml of Krebs—Ringer—bicarbonate 
buffer containing L-tyrosine (I x 1o-# M). 

Intracellular concn. (g/ml) 


Compounds 
Medium concn. (g/ml) 
Control 2.63 
+ 2,4-Dinitrophenol (10-3 7) 28 
+ 2,4-Dinitrophenol (10-* M) + 
glucose (10-2 MW) 2.85 
+ Iodoacetate (10~? MW) 1.69 
+ Iodoacetate (10-2 M) + 
glucose (10-2 M) 2.57 
+ Cyanide (10~* M) 1.01 
+ Azide: (107% 7) 1.48 


References p. 553 
