ABSORPTION OF AMINO-ACIDS 93 



acid will exchange with extracellular isotopically labelled 

 glutamic acid in the absence of metabolic energy can be 

 explained if there is a carrier mechanism of this type in the 

 cell membrane. All these theories are purely speculative and 

 their acceptance or rejection awaits the results of further 

 experiments. One fact of which account must now be taken 

 is that the accumulation of glutamic acid within ferment- 

 ing cells of Staph, aureus, Strep, faecalis and Sac. fragilis is 

 accompanied by an increase in cellular K"^, the increase 

 appearing to be of the order i gram atom K'^/mole glutamic 

 acid [lb]. 



The full significance of the ability to absorb and accumu- 

 late amino-acids still awaits complete evaluation since only 

 three organisms and a restricted number of amino-acids 

 have so far been investigated. It may be remarked that a 

 decrease in the nutritional requirements of Staph, aureus is 

 accompanied by a decreased ability to accumulate amino- 

 acids [12], but it must also be noted that Sac. cerevisiae is 

 not exacting towards amino-acids and yet accumulates many 

 of these compounds [19]. Moreover, washed suspensions of 

 a large variety of organisms, Gram-positive as well as Gram- 

 negative, decompose several amino-acids, the implication 

 being that unless the appropriate enzyme is in the cell 

 surface the amino-acid enters the cell by free diffusion. 



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