J. T. HOLDEN 
On 
NI 
iS) 
The rather strict structural requirements cited above are not uniformly encountered. 
Thus, the D-isomers of methionine in Alcaligenes faecalis®, phenylalanine in S. cere- 
viseae* and tryptophane in E. coli? reduce accumulation of the corresponding L- 
amino acid. Broader specificity of the S. cereviseae systems is indicated also by the 
ability of valine to reduce phenylalanine accumulation and of phenylalanine and 
methionine to reduce valine accumulation. In such cases however, extracellular 
peptide formation does not seem to have been excluded as a cause of reduced accumu- 
lation. N-methylvaline and valine amide were inactive as inhibitors demonstrating 
again that both the amino and carboxyl groups are required for activity. 
In £. colt accumulation of small amounts of proline from very dilute solutions is 
highly specific, being unaffected by a mix of fifteen amino acids each of them present 
at a concentration 100 times higher than proline!®. When the concentration of extra- 
cellular proline is raised, much larger pools accumulate and competitive interactions 
are evident. On the other hand, these workers also encountered competitive inter- 
actions between isoleucine, leucine and valine at very low extracellular concen- 
trations}, 
Confirmation of the structural specificity of some accumulation systems is found 
in the behavior of so-called transport mutants. The limited data available so far 
show that mutants incapable of accumulating D-serine also fail to accumulate L- 
alanine and glycine, while those incapable of accumulating canavanine accumulate 
alanine and glycine normally but accumulate subnormal amounts of L-arginine, 
L-lysine and L-ornithine!®. LuBIN et al.®® also have presented data suggesting speci- 
ficity of amino acid accumulation in transport mutants. 
Peptides are taken up rapidly by bacteria but apparently by routes independent 
of those responsible for amino acid uptake. In F. coli valine peptides do not interfere 
significantly with valine retention®! suggesting that they do not interact with the 
valine accumulation system. Since these peptides support growth of valine-requiring 
strains, it is likely that a separate system exists for their uptake. LEACH AND SNELL® 
showed that glycine peptides are taken up more rapidly than glycine by Lactobacillus 
caset. The peptides do not accumulate as such but are hydrolyzed rapidly. The 
possibility exists that this rapid metabolism may account for the superior rate of 
uptake compared to the free amino acid. An E. coli mutant with a reduced ability to 
take up glycine grows well with glycine peptides again suggesting the existence of 
separate uptake systems for this amino acid and its peptides®*. GALE and his co- 
workers also observed glutamate accumulation during exposure of S. aureus to a 
variety of glutamyl peptides, but the relation to the glutamic acid accumulation 
system was not established. 
Requirement for energy 
The dependence of glutamate accumulation in L. avabinosus on glucose metabolism 
is illustrated in Fig. 2. In this organism and S. faecalis all amino acids studied so far 
have been found to accumulate in large quantities only in the presence of a ferment- 
able carbohydrate*, ®4, Requirement for an energy source has been reported in many 
other investigations, e.g. in S. aureus (glutamic acid)’, in yeast (glutamic acid)™}, 
(various amino acids)*! and in EF. coli (proline)!8, (various amino acids)?!. In some 
cases, endogenous reserves appear to suffice as for a-aminoisobutyric acid accumulation 
References p. 592/594 
