AMINO ACID TRANSPORT IN MICROORGANISMS 581 
surface of the membrane, or by neutralization of a protecting substance and that 
the apparent influx of water is not solely or even principally attributable to the os- 
motic activity of the accumulated solute. The enhanced stability of bacterial proto- 
plasts in the presence of basic substances such a spermine’? is consistent with this 
view. Thus, while the likelihood is great that at least a portion of the intracellular 
amino acid pool is osmotically active, the force of this evidence could hardly be con- 
sidered as overwhelming. 
Dependence of accumulation on osmotic factors as a function of physiological 
and nutritional status 
Additional evidence suggesting that accumulated amino acids in L. avabinosus and 
S. faecalis may be osmotically active was encountered indirectly during our studies 
on the effects of various nutritional deficiences on the accumulation process. Stimu- 


T T =alis 
van 
poe i 
60 , 
1 HBgCELLS 
asin apg | 
------~. 


pmoles GLUTAMATE / 100 mg CELLS 

MINUTES 
Fig. 5. Effect of vitamin B, deficiency on glutamic acid accumulation by L. avabinosus. See ref. 47 
for experimental details. Glutamate content of cell extracts measured isotopically (———) and 
by enzymatic decarboxylation (———-). 
lated by the provocative finding that pyridoxal increases the amount of amino acid 
accumulated by mouse Ehrlich ascites cells!®; *°, glutamate accumulation was com- 
pared in nutritionally normal and vitamin B,-deficient cells of L. avabinosus > *4. 
The results illustrated in Fig. 5 show that the initial rate of accumulation is not 
modified by the deficiency, but that there is a large decline in the amount of amino 
acid which can be retained. This and other evidence contra indicated a catalytic 
function for vitamin B, in amino acid accumulation (this is true also for S. faecalis). 
Furthermore, the large change in capacity appeared to be an indirect effect, not 
attributable to the direct involvement of vitamin B, in the uptake process*’. 
Subsequent studies showed that vitamin B,-deficient cells were morphologically 
abnormal*®? and that they leaked unusually large amounts of intracellular nucleotides 
during incubation in phosphate buffers*®. Suspecting a cell wall defect with secondary 
alterations in permeability properties, osmotic aspects of the accumulation process 
were investigated. It was found*® that the addition of high concentrations of sucrose 
and other substances to the incubation buffer permitted essentially normal glutamate 
accumulation by severely vitamin B,-deficient cells. Fig.6 shows that precisely 
References p. 592/594 
