ABSORPTION OF AMINO-ACIDS 9I 



anion. Even though the latter takes place, there may be 

 another mechanism which excretes an equivalent amount of 

 either the same or a different anion together with cations to 

 replace the lysine absorbed. It may be recalled that fer- 

 menting yeast absorbs K"^ from a medium containing KCl 

 and replaces it by H"^ [see 20]; there is apparently no uptake 

 of Cl~. A possible explanation here is that metabolic energy 

 is used to form H"^, which is then secreted into the medium 

 in exchange for K"^, thus making it appear that the uptake 

 of K"^ is an active process, i.e. dependent on metabolic 

 energy. It may therefore be suggested that lysine is absorbed 

 by Strep, faecalis in exchange for cellular K"^ or another 

 cation which does not have to be formed at the expense of 

 metabolic energy. However, recent work dealing with the 

 accumulation of lysine showed that in Strep, faecalis it was 

 accompanied by a gain in cellular K^ (with no significant 

 change in cellular Na"*") whereas with Staph, aureus it had 

 no apparent effect on either the K"^ or Na"*" content of the 

 cells. In Saccharomyces fragilis, the uptake of lysine was 

 dependent on glucose fermentation and was accompanied by 

 the loss of Na"^ and K"*" from the cells [ib] (in none of these 

 experiments was the migration of 0H~ and H studied). 



Mechanism of glutamic acid absorptio?i 



Having regard to the second explanation (ii) advanced 

 above, it might be suggested that the 'free glutamic acid' 

 of the cell is in the form of glutamine, a substance whose 

 synthesis is endergonic and which is assayed by the decar- 

 boxylase preparation as though it is the free acid: moreover, 

 as glutamine cannot freely diffuse into cells, it is possible 

 that it cannot itself pass through the cell wall [5]. But only 

 a small part of the glutamic acid of the internal environment 

 of streptococci is in fact in this form [14]. Hence the energy 

 associated with the uptake of glutamic acid may be used in 

 the manner outlined in the last two explanations, iii and iv. 

 The former of these proposes that active transport, i.e. trans- 

 port dependent on metabolic energy, involves chemical 



