AMINO ACID TRANSPORT IN MICROORGANISMS 577 
insensitive to penicillin, since it functions normally when the cell is protected by 
sucrose, or in a cell containing sufficient quantities of wall substance. Reduced 
accumulation in the presence of penicillin appears, therefore, to be a secondary effect 
caused very likely by a primary interference in cell wall formation. HANCOCK" also 
has reported that the inhibitory effects of penicillin on amino acid accumulation in 
S. aureus can be prevented by adding sucrose to the incubation medium. 
GALE observed little or no inhibition of glutamate accumulation by chloram- 
phenicol and some inhibition by aureomycin at concentrations which did not signi- 
ficantly interfere with glycolysis*®. In L. avabinosus chloramphenicol has consistently 
shown a small stimulatory effect on glutamate accumulation. Streptomycin causes 
leakage of intracellular constituents in sensitive strains of FE. coli4. Damage to the 
permeability barrier of the cell is suspected and the effect is accompanied by a 
marked decline in ability to accumulate exogenous valine. Other antibiotic!? and 
antifungal’? compounds have been observed to cause leakage of intracellular consti- 
tuents. It would be of interest to determine whether amino acid accumulation also 
is affected in these cases. 
In L. avabinosus bacitracin, tyrocidin and gramicidin reduce glutamate accumu- 
lation markedly. Gramicidin, but not tyrocidin inhibition, is reversed by high levels 
of sucrose. Tyrocidin was shown by GALE AND TAYLOR?’ to release accumulated 
glutamic acid from S. faecalis cells presumably by disruption of the cellular perme- 
ability barrier. The steroid, deoxycorticosterone, reduces the ability of germinated 
Neurospora conidia to take up various low molecular weight constituents including 
inorganic ions and amino acids®. Subsequent studies have indicated that rubidium 
uptake occurs in two phases, an energy-dependent entry step followed by a binding 
step®*. The latter process is believed to be inhibited by deoxycorticosterone. A 
comparable analysis of amino acid uptake, unfortunately, has not been reported. 
In our studies on glutamate accumulation deoxycorticosterone had no inhibitory effect 
in L. arabinosus. 
As yet, inhibitor studies have not provided definitive clues to the nature of the 
accumulation system. A recurrent observation, that compounds which promote 
leakage of cell constituents also reduce accumulation, suggests that a functional 
permeability barrier is essential for the accumulation of large amino acid pools. 
Miscellaneous observations 
BRITT AND GERHARDT, during a study of lysine accumulation in cells and protoplasts 
of Micrococcus lysodetkticus®, observed that a sizable fraction of the “pool” was 
adsorbed in the cell wall!®. This underscores the importance of showing that any 
charged solute, such as a basic or acidic amino acid, does in fact occupy an intra- 
cellular locus when it is accumulated or thought to distribute in cellular water. 
Changes in cell volume and methionine accumulation activity are not correlated 
in cells of Alcaligenes faecalis undergoing synchronous division®?. Accumulation 
activity was found to remain constant per cell throughout the division cycle indicating 
that synthesis of the accumulation machinery was closely synchronized with the 
reproductive process. However a sizable increase in accumulation activity per cell 
was observed when stationary phase cultures were incubated in growth medium 
prior to the onset of exponential growth. 
References p. 592/594 
