ABSORPTION OF AMINO-ACIDS 87 



between the internal and external concentrations at equili- 

 brium were similar to those found for lysine (cf. Fig. 6.2). 

 But, in contrast to lysine, the rate of uptake was not directly 

 proportional to the external concentration (Fig. 6.1) and 

 the relationship was reminiscent of that between the rate 

 of an enzyme reaction and the concentration of the sub- 

 strate. The Qjo over the range 2o°-30° C. w^as 1-94, which 

 is close to 2-0 and therefore indicative of a chemical and 

 presumably of an enzymic reaction. 



Various inhibitors of intermediary metabolism, such as 

 cyanide and iodoacetate, have no effect on the uptake of 

 lysine, but any substance inhibiting fermentation also 

 inhibits the uptake of glutamic acid. However, it is possible 

 to separate the processes of energy production from those 

 of energy utilization by preferential inhibition of the latter. 

 This may be accomplished by using a substance such as 

 8-hydroxyquinoline which in low concentrations inhibits 

 the uptake of glutamic acid without affecting fermentation, 

 although higher concentrations inhibit the latter as well [7]. 

 Since 8-hydroxyquinoline is a chelating agent, the conclu- 

 sion was drawn that cations played an important role in 

 glutamic acid absorption. Staphylococcus aureus was used in 

 these experiments and the problem was further investigated 

 by growing the organism in the amino-acid poor medium 

 from which one or more cations had been removed. The 

 ability to absorb and concentrate glutamic acid was seriously 

 impaired only in cells harvested from media deficient in 

 Mg"^"^ or Mn"*""^. Whilst there is insufficient data for 

 deciding which of these ions is the natural activator of the 

 glutamic acid absorption mechanism, it is pertinent to note 

 that both of these cations are frequently found as co-factors 

 of enzymes associated with phosphorylation. 



In view of the dependence of the process on metabolic 

 energy it is conceivable that glutamic acid passes through 

 the cell wall in the form of a compound whose synthesis is 

 endergonic (e.g. as glutamine, glutathione, or a phosphory- 

 lated derivative), and having passed through the cell wall, 

 this compound is reconverted to the free acid. Glutamine, 

 glutathione and glutamylglutamic acid all failed to enter 

 7 



