AMINO ACID TRANSPORT IN MICROORGANISMS 573 
in B. megatertum™. GALE has studied energy-yielding substrates other than glucose 
and observed that pyruvate and arginine have some activity in S. aureus*!. This 
group aiso has studied the ability of various glutamate derivatives to permit the 
intracellular accumulation of this amino acid in the absence of fermentable carbo- 
hydrate!4. N-phosphorylglutamate and diethylglutamate had some activity although 
the rates were inferior to those observed when the cell was exposed to glutamic acid 
and glucose. None of a variety of glutamyl peptides led to intracellular glutamic acid 
accumulation in the absence of an energy source. Since the accumulation of glutamate 
derived from N-phosphorylglutamate was sensitive to DNP and azide GALE suggested 

™— T 
1 
a 

20 

[umoles GLUTAMATE / {00 mg CELLS 
eo 


qe moe —” 
! 1 3 
fe) 30 60 90 
MINUTES 
Fig. 2. Effect of glucose and reduced incubation temperature on glutamate accumulation by 
L. avabinosus. Glutamic acid of cell extracts was assayed by enzymatic deca1boxylation and 
radioactivity. Standard uptake conditions®? with, curve 1, /\ A, glucose present; curve 2, 
@ —@, glucose omitted; curve 3, © —), glucose present, incubated at 2°. 


that the breakdown of this compound might yield energy for its own transport or of 
the liberated glutamic acid. Apart from these few observations there is as yet no 
evidence indicating the manner in which energy-yielding reactions are coupled to the 
accumulation process. 
Evidence for energy dependency in transport is also provided by studies showing 
the inhibitory effect of uncoupling agents such as DNP and azide as in the accumula- 
tion of tryptophane’, and other amino acids! by E. coli and of various amino acids 
by S. cereviseae*! #2. It must be recognized that these substances may react in many 
ways within a cell and that specific interaction only in phosphorylation systems 
cannot be assumed. A number of investigators have in fact observed anomalous 
behavior with these substances. GALE®® found that DNP and azide at some concen- 
trations markedly increased glutamate accumulation by S. faecalis. As in previous 
studies with triphenylmethane dyes*® this was attributed to a differential effect on 
competing reactions which normally consumed accumulated glutamate. Using iso- 
topically labeled glutamic acid we have observed a marked resistance of glucose- 
dependent glutamate accumulation in L. avabinosus to DNP and azide inhibition 
except at high levels (DNP, 30% inhibition at 0.01 MW; azide, 30° inhibition at 
0.03 M). At lower concentrations there is a pronounced stimulation of accumulation 
References p. 592/594 
